Feminism since the 1970s has been advocating for financial independence for women so that they can leave someone regardless of how much they earn.

Yeah see, women have gained gender roles that aren't the traditional, but the traditional homemaker is still an option. A woman can say "I want to be an insufferable boss bitch" OR she can say "I want to be a homemaker and let a man pay my way my entire life." Men do not get that kind of option; a man doesn't get to say "You know what I'm just gonna find a wife who will pay all my bills for me." That shit doesn't work. Your neighbor or whatever who's a stay at home dad? I guarantee that's not how he made his case on a first date because there wouldn't have been a second one. I've seen women go on Tinder under a man's account and try dating as a man, it's an eye opening experience for a lot of them. Make up a profile that says that. "I want to be a stay at home dad and have my wife be the sole breadwinner" and see if you get ANY attention. I guarantee you won't.

then first, I’d point out that’s a stupid definition,

I would agree with you here. Measuring a man's success as his ability to get and keep a woman is kinda worthless. A man can do everything right and still get left because she's bored or thinks "an accountant is good but maybe I can find a lawyer." Women love divorce, after the wedding ceremony it's probably their favorite thing about marriage. Comparing the divorce rates of gay men, heterosexual couples and lesbians, gay men get divorced the least and lesbians get divorced the most. You seem to be pushing a hypothesis that divorces are caused by men behaving badly to their spouse, but if that were the case you'd think that gay men would abuse each other the most and lesbians the least, when the opposite seems to be true.

BUT HERE'S THE THING. The traditional gender role of a man is to be a breadwinner and provider--for himself at least--if not a wife and nuclear family, right? That's the traditional man's role. Work and earn a living for yourself and your dependents. The traditional male gender role includes bachelorhood be it temporary or permanent.

To step outside of that role pretty much means you're not going to pay your own way, in which case where is food and rent going to come from?

Government welfare? In third world failed states like the USA this is unlikely and getting less likely each administration.

Living with his parents? Grown men who are still dependent on their parents are always the butt of a joke. "Parent's basement" is synonymous with "pathetic loser" and you'll see people call men who are dependent on their parents pathetic to his face even when they've come to him for help with something because he's probably handy with electronics.

A breadwinning wife? Reversal of traditional roles, she brings home the bacon he cooks and cleans? Well to do this, he has to attract and keep a woman. By fucking definition. If he doesn't, this strategy has failed. BY FUCKING DEFINITION.

Breadwinning husband? Straight men are locked out of this one.

Homelessness. Need I say more?

Prison. Also, need I say more?

Can you think of anything else for a man to do? No. It's go to work and support himself.

Now that we're in the workplace, you'll find men are being pushed in a more masculine direction, not less. Women enter the workforce almost entirely in safe, indoor, climate controlled jobs. Women are rare to find in infrastructure, mining and logging, construction, transportation, so on and so forth. Men do the dirty and dangerous jobs and increasingly that's all that's offered to them.

What choice of gender role is there for a man? In the 1950's you had husbands and wives. That's it. The man went to work and brought home the money, the woman stayed in the home and did housework and cared for children. In the late 20th century feminism happened and you get the Liberated Modern Woman(tm). Women suddenly had choices. Men saw no such change. There is no such thing as the Liberated Modern Man(tm). I'm probably the first person in history to have typed the phrase.