Mainly economics, although it has some relation to what the parent post is talking about. Unfortunately the sexual revolution happened in the US about the same time when labor unions got fucked, labor power got diminished due to globalization/deindustrialization/automation, and people started be compensated less dollars per productivity. In an ideal world where Keyne's prediction was right, we (both genders) would work only 15 hours a week due to technological advancement and spend the rest on taking care of famliy and community (including special considerations for women on pregnancy), but it seems that these lower-working-hour dreams haven't come true. But then there's an even more insidious cultural part of neoliberalism: for an increasing number of people you're not just supposed to just do your job, you have to indulge in it to prove your self-worth to the boss, you need to advance and maintain your "career", and have to race to the bottom to get a clutch on getting a chance of moving up the social ladder (or else you're going to work at a call center or increasingly precarious part-time gig jobs). Kids are just a liability in this hyper-competitive world; no wonder why women aren't going to have kids, when every aspect of society is telling you (in indirect ways) not to.

Agree that the artificial womb is an undererstimated milestone technology that will radically change the world. But such a technological solution isn't a perfect solution for low birth rates if you take care of the fact that you still need to take care of the kids born out of these artificial wombs (even though it could radically improve women's lives).