Ignorance and gullibility. I fall for misinformation all the time, especially when it confirms my own biases and it takes real effort to maintain a mindset of "yes this sounds true, but is it actually?" It is also terribly inefficient. If someone tells me, when I was a kid, that daddylonglegs spiders are the most poisonous, I am likely going to just go "neat" and now I think that and say it. If you stop and verify EVERYTHING EVER you have no time to do anything in life. This makes the filter of critical thinking.....critical.

Also, it isn't about being stupid (though that helps). Some of the smartest people I know are conspiracy theory nutjobs. They can easily draw parallels between disparate facts, but can't filter their findings or understand correlation doesn't equal causation.

They're idiots

The rich are clever and very well coordinated

Often when I see someone accusing people of voting against their own interests, it's pretty clear that the person making the accusation has not taken the time to understand the values others are basing their choice on.
If I could rob a person and be confident that I would never be caught and punished for doing so, am I acting against my own self interest if I chose not to rob them because it goes against my moral code? No, of course not. But based on the way some people talk about voting against ones self interest, you might think I just cheated myself out of free money. Is it possible that a person might "vote against their own interests" because of a misinformed view? of course, but you'll never understand a person's motivations by chosing to paint them with broad strokes based on your prejudices instead of getting to know them individually and trying to understand what it is they truly value.

Probably unpopular answer, but it's not some clear cut "this political party has better policies for everyone". Republican policies usually are better for people living in rural areas, and Democratic policies are usually better for people in cities. I'm sure people will debate this, but this is the reason why people typically vote depending on where they live. At the very least, they believe that their party has better policies for them and their way of life.

My personal (anecdotal evidence) is that I work for a small business in a rural area, and our main customers are other small business owners (usually self employed or under 5 employees). Over the last 3 presidents, the Obama years were rough for our company, we had explosive growth during the Trump years, and then we've had stagnant growth over the past 4 years. Our largest competitor went out of business this past year, which sent us a lot of new customers, but we've also had a lot of our customers go out of business as well, so we've been pretty stagnant. Being stagnant isn't terrible, we don't have shareholders or anything, but the cost of living has increased and company profit/wages haven't which is a problem. That said I know we're doing pretty well compared to a lot of people here.

Another (once again anecdotal) example is that I have a friend who paints murals full time, for the past 30ish years. He told me that he does well with either Republicans or Democrats in office, but that his customers change. During republican presidents, his customer base is usually local businesses wanting to decorate their stores. During democratic presidents, his customer base is usually towns, state buildings, schools, etc.

But anyways, I'd be very interested to hear from some people living in cities if there's a visible uptick in income/etc when we have a democratic president, or in general what your personal observations are on how which president affects your local businesses/income/prices/etc.

False consciousness.

Because they've successfully been conned into thinking that what's in the best interests of the rich is in their own best interests too.

Manufactured consent

They believe it will benefit them one day.

I can use my brother as an example for that:

My younger brother is entirely sold on billionaire philanthropy. He watched interviews where people like Elon Musk and Jeff Bezos on talk shows and podcasts, places where people like this go to advertise themselves, and has been completely convinced that they're innovative, smart people.

Smart people who, through just being so damn smart, managed to become billionaires.

Who is there to vote for otherwise? Two sides of the same coin. The rich try to keep politics about anything except wealth inequality. The rich keep the good candidates off your ballot long before it’s time to choose between tweedle Dee and tweedle dum.

The sooner you realize the vast majority of humans are simply not very intelligent, the more everything starts making sense. And the more depressed you will be.

Bexause you have a two party system where both sides are corrupt

It's hard to vote for one candidate that represents all your values or interests. Typically every candidate will be against your own interests in some manner. Preferential voting systems mostly curb this issue by allowing you to select many candidates in order of preference.

https://www.cracked.com/blog/6-reasons-trumps-rise-that-no-one-talks-about

its not about red vs blue states. It's About The Country Vs. The City

A successful propaganda campaign by the owning class.

And a quote from an anonymous mutual:

many people will unfortunately need to learn this the hard way it seems at the expense of those who take the time to see the writing on the wall those ignorant to their exploitation will seldom listen to those who try to tell them how horribly theyre being fucked "if it were really so bad id notice" theyll say "this isnt so bad" theyll say, standing on the peak of the mountain that is dunning-kruger unknowing all we can do is wait, and watch to find out what what it is that throws them into the valley of unfathomable uncertainty in the meantime we must work for each other, for those who do see how good things could be. maybe then, our greener grass will coax them into giving us a fair listen

Something to consider is not everyone's interests are aligned. I'm not American so I can't comment on that specific area of the world, but that sort of question comes up a lot in my country and one of the biggest reasons is one party wants to make my hobbies/job harder and the other doesn't. So I don't think I'll vote for them. Now you, someone who doesn't have said job or hobbies, probably doesn't give a fuck about that. So you support said positions.

A lot of people have aspirations of themselves being rich and if they can vote like rich people they participate in the rich aesthetic.

Because it's no longer about benefits or interests.

It's about the "my side won, your side lost, get over it" mentality. It's about the tribalism and making sure you keep your ire focused on your fellow man rather than looking up and seeing the source of your problems

And it's not just the US. It's fucking everywhere.

Kind of an indirect answer, but I've heard people state that they vote against their own personal beliefs because they think that there needs to be a balance between "good and bad". Obviously, this is complete bullshit. Even if there should be a "balance", we already have enough problems as is, we don't need the government making it worse.

TL;DR: I blame FPTP.

Hm, I'd argue that this is a byproduct of the spoiler effect — I think it's due to strategic voting. I think that it's likely not due to people consciously voting against their own interests to benefit the rich (assuming that they indeed do this ­— ie that voting to benefit the rich is against their interests), but instead that the entities that support these sorts of beliefs, also tend to align with other beliefs that are more important to the voters, and "benefiting the rich", while possibly perceived negatively, is a sacrifice that the voters are willing to make.

• Because propaganda works. If propaganda didn't work, companies would not advertise products and politicians wouldn't run campaigns. Rich sponsors fund politicians who promise to look after their interests. Well-funded politicians run better campaigns and win.

• Because politicians are, nearly without exception, above middle class, if not outright rich. They won't act too radically against their own class interests.

The only solution I know comes from ancient Athens. Sortition -> you hold a lottery to draw representatives. A few extremely stupid people will be drawn into parliament, but idiots are far better than sociopaths, and the current system gives undue representation to sociopaths (willing to climb over bodies if that gets them to power). If one then dislikes the idea of a considerable percentage of bumbling fools (as opposed to cunning predators) in parliament, one must feed everyone well, treat all childhood diseases and educate everyone as well as possible. As if their rational decisions were needed tomorrow.

Most are wanting an end to this current system so they’ll ‘play’ it out knowing albeit the struggle, Democracy has left the building and late stage capitalism is showing the disparity of the predators and preys of society

What would be an example of this? It's not obvious to me that by simply voting in a manner that benefits "the rich" then also means it's against your own interests. When someone gains something it doesn't mean I must lose something in exchange.

Since I didn't see it listed yet, fear of change.

Some folks are just fearful of change.

Rarely is a change proposal black and white. We can show you good data to support the change. We can look at it from a reputable source. We can look at how the change affected others. We can agree it's most likely a good change.

But sometimes we fear it.

What if we're wrong?

I think that it depends on the person. I've heard of enough people who voted for Donald because they like that he "says it like it is", or "he's a businessman", or because they just want lower taxes. Some people are so exposed to rage-bait social media/news content and are always being told what to be afraid of and they vote emotionally based on that fear. My grandfather votes the way he does because he's TERRIFIED of immigrants, even legal ones - because all he does is sit and watch fox news. I think most often, people are busy with their lives, paying their bills, taking care of their kids, etc. and don't have a lot of energy left over for politics. People treat voting like it's team sports. A ton of people voted for Donald because they thought tariffs were paid by the other country, not American businesses. I don't exactly blame people, it's a lot of information and life is probably a lot more relaxed for people that don't follow it.