* If you keep your baby, you are nearly-guaranteeing hunger of your family or your village in 10 years or so. And people in your community would hold a grudge against you and your child for it, from day one.
* The cultural norm regarding when life is sacred was different. Many people in the US believe in-womb abortion is not particularly enlightened either.
Japan during much of the Tokugawa period (after 1700) is an example of that kind of self-stabilizing population. They used:
* Abortion
* On-birth infanticide (don't be quick to judge)
* Delayed marriage (which also means more years of celibacy before marriage I guess?)
https://international.uiowa.edu/sites/international.uiowa.ed...
and AFAICT this was not government-enforced or even strongly-government-encouraged.