people don't like to address the elephant in the living room, it's not financial matters that affect the declining birth rates, but materialism and hedonism. so the solutions offered to the problem are materialistic themselves, let's give people money to have kids and similar stuff, but people can't be arsed for those above mentioned reasons. extremely poor people have more kids and they also tend to be more religious, and people in old times were much much poorer than nowadays average joe, yet they had more kids, they were way less secular as well.
Argentina