> But maybe in other poorer countries it's something like "having sex is the only pleasure I get in this unbearable hellscape of an existance"

Also, in poorer countries, having kids becomes a necessity for survival. Places without safety nets, elder care, etc. You have kids to both take care of you as you age, and also as labor to help with survival.

That pressure/need doesn't exist in most of the west, so that incentive is gone.