>>82409003
First if all, overpopulation. Where there is too many people around we are exhausted from interacting with them and choose not to make more social work for ourselves. This is a natural biological mechanism, because ancient humans had to strictly control their populous to survive
Second, realistically average family had around 5 kids. Anything more was considered a huge burden. There were 10+ births, commonly, but few survived into adulthood.
Third, urbanization. Children are a not profitable in an urban setting, simple as. From asset on field, they turn into competition for assets such as money and living space. Cities are antagonistic to human natural environment and thus demotivate reproduction. We are animals in a captivity, doe. Check out urbanization levels and birthrates. The link is quite straightforward
