Not having kids and having less kids is a universal trend that is not unique to America. It's affecting every country in the world, and the US is actually doing better than most at the same level of development.
Bangladesh’s decline in fertility rate is due to deliberate population control efforts over the last 70 years. (That was my dad’s career. We came to the US because he was working on a USAID population control program in Bangladesh.)
You can see this clearly by looking over at Pakistan, which has almost double the fertility rate despite being at a similar level of economic development. If it was dictated by economics rather than culture and policy, you wouldn’t see that.
It's also affecting Bangladesh.
https://www.macrotrends.net/countries/BGD/bangladesh/fertili....