Believe it or not, they aren't always available. Seriously. Well, not available and in good state.

If you go to some places, usually "bad" areas in cities and very rural small towns (or just rural without any town at all), you end up tempting relying on single source for food. It might be something as relatively useful as a proper bodega, but it can be a gas station instead. Even if the place does stock those staples, they will sit there until they get sold, or get so far past the "sell by" or "best by" date that the owner finally throws them away. So you can go in looking for that stuff, and then it's so damn old that it doesn't cook right.

Even out here in the mountains, where you can usually have a small garden, you run into serious issues obtaining other staples to make a complete food source, much less make food be more than just fuel, which can be soul crushing and lead to disordered eating on its own when people do run into a chance to splurge.

Food deserts are a thing, and they drive malnutrition as well as obesity.

That level of scarcity is way more common than people think for those living under the poverty line. And even that assumes that the individuals can cook. You've got the disabled that may not be able to, you've got people that don't how how. Even when that isn't in play, you can run into shitty apartments/rentals that make it difficult to cook no matter what. Places where a stove can be out of order for months without being fixed or replaced, and likely replaced with something that doesn't work right.

Beyond that, why the fuck is the assumption that the people have been given any kind of nutrition education to know what they can buy that's healthy? Why is it assumed that living on beans and rice is a good state of being?

It's real easy for those of us that have had the privilege of good nutritional education to assume all kinds of things, but that doesn't make the assumptions correct

Btw, that got ranty at the end, it wasn't directed at you, it's the situation that's the infuriating thing.

One reason is the more you're forced to work, the less energy, and, more importantly, time you have for preparing healthy meals. Therefore you're more likely to go with preprocessed, prepackaged meals or straight fast food which will make you fat fast.

I've got a relatively cushy job and cook my own, relatively healthy meals but even I find myself going for that store-bought pizza when I have a particularly busy week.

Moreover, unhealthy, preprocessed meals are basically drugs in terms of the dopamine hit, so you're more likely to go for them if your life sucks and you're sad about it.

Add to that the lack of education on healthy eating, which I'd bet is easier to come by when you're at least middle class and bam, you're a fat poor person.

They're bland and people want to enjoy life - rice and beans is good enough to support life (but stingy in some nutrients) but people want to enjoy food.