All those countries had intense anti-natal campaigns by the government. They didn’t outright kill babies like China, but they persuaded two generations of people to closely link the idea of lower birth rates to development and civilization: https://www.firstthings.com/article/2023/05/anti-natal-engin...

This was supported by intense efforts from western countries to reduce birth rates in Asia. Family planning and contraception promotion is a key segment of USAID, for example.