Libfeminism in the US prefers going after large, controversial, vaguely defined problems because they don't require a lot of hard work or coordinated organising to deal with, and they can piss off conservatives by shouting about their vagina. You can go out and have a protest about slut shaming or abortion or pussy grabbing and people will get excited about it because it's a big abstract thing which gets people mad, but tackling something like the lack of paid maternity leave would require knowledge of the subject and a hard look at the way american companies treat their female employees. It would also mean adressing that fact that women take more time off work than men due to maternity, which would harm the argument about the pay gap.
Plus, companies can say 'we support a woman's right to choose' or 'the president is a pussy grabbing douchebag'! and not lose anything, but supporting paid maternity leave would mean having to actually pay their workers reaosnably, so there's less corporate support for the maternity pay cause and thus less money being channelled into organising.
There are feminists in the US who care about real, serious, concrete women's issues and inequalities like this, but their protests don't attract nearly as much attention because the issues aren't sexy or divisive. Women not getting paid maternity is just a sad reality of the way that companies and employers piss on the workers, especially blue collar workers, and you can't make a sassy sign or knit a pussy hat about that. Feminists should work with the unions to make a stink about the maternity leave. They might have more of a chance, then.