My theory is that once you get a sufficiently outraged group of people on a righteous crusade (historically, we've treated women pretty badly in the USA), that

My theory is that once you get a sufficiently outraged group of people on a righteous crusade (historically, we've treated women pretty badly in the USA), that righteous outrage does not dissipate once the primary causes of that outrage have been addressed. As a result, you get more and more minute nonsense being shoveled into the ideology (example: the "manspreading" idiocy) that's attacked just as vigorously as actual things that cause actual problems, like discrimination and human rights. Then, the movement sufficiently de-legitimized due to this, more and more unaffiliated people turn against it, and some of their gains are lost.