From my observation in my social circle, there are two pressures that forcing not having kid or more kids. One is support system and second financial stability to take care or kids.

First, with both partner working & almost no one to support(from relatives/close family) during first 3-5 years of kids. It's super exhausting and one starts having second thoughts about having more kids.

Second, People want good future for kids. Daycare expenses, school, college etc. general thinking is if I can support one child really well and not two then its better to have just one.

In my experience I have not seen anyone who genuinely dont like kids or regretted having kid even at their emotionally lowest point. It just above two primary forces, pushing them towards not have anymore kids.