Work expectations to maintain these debt driven economies are a huge factor too. A lot of the Asian countries you mentioned have a 9-9-6 work philosophy, or something similar. Kinda hard to make a baby when those are your working hours, much less raise one. What's the point? You'd be able to spend more time with the goldfish on your office desk than your own flesh and blood. So why bother having a child, where now the only benefit to doing so is the joy of having one to raise, when you'll hardly ever see him/her? You won't have the time.
Another point from a woman's perspective. You briefly mentioned it; kinda skirted around it. In the 18th and 19th centuries having babies was risky business. Literally every pregnancy was Russian Roulette with your life or your health. There was a lot more mortality of mothers as well as children. Things got better in the 20th century as medicine advanced, but also being able to space them out meant more recovery time for mom.
These days, we've got a couple of things going on. The Roe v. Wade decision meant if things went horribly wrong, women didn't have to risk their lives to be pregnant. The security of having abortions safe and legal meant that women were secure to have children. Particularly multiple children. You don't have to potentially orphan a child(ren) you've already had in order to have another one.
Well that's gone now. I guess time will tell if it has a tangible effect over all in how many children women choose to have. My guess is that it will. We're all seeing in the post Dobbs discourse that many women being denied abortions for medical reasons already have older children that are also at risk of losing a parent or losing stability because of the bans. I'd be willing to bet that a lot more women are going to stop at one rather than risk their lives or stability, should things go wrong.
Although modern medicine has mitigated a lot of the risk of childbirth, it hasn't eliminated it. Something like 42% of pregnancies in the US meet the criteria for being classified as high risk of complications. And now, no intervention when things go bad.
