It is similar to other countries getting rid of "no fault divorce" or abortion access.

By making the strict cutoff early, you have women who genuinely do want kids much more likely to do it with the nearest guy they can find and while their careers aren't stable enough to really recover from a pregnancy. Which then traps them in the marriage and means they continue to be barefoot and pregnant in the kitchen for the rest of their lives.

I saw it play out in grad school far too many times. Women who wanted families would start early (and there are actually very strong health reasons to not wait until your mid-late 30s). And even with our advisor being very understanding... it is a massive derailment at a time where even a two month delay can be the difference between being cited for a foundational concept going forward and having to start over because someone else published. Same for getting internships that can lead to jobs and so forth. Which leads to "oh it is just too hectic right now. I'll go back to school when my kids are old enough to not need me all day"

But even five or six years later? Both partners have a solid salary. So it is still a big hit to have diminished capacity for the third trimester and then maternity leave but that kid goes into preschool and things get back on track pretty quickly.

But... then you have one or two kids. Rather than the person who gave up on a career and is a stay at home mom (and no shade to people who DO want to do that) where it is "easier" to have more.