Why are less people having kids these days?

That's not the only reason to get married. The main reason for marrige is that you love each other. Maybe they know that the world is getting over populated. If there was a law that you had to have children then people would have them but they would kill them and say "Oops." But they wouldn't feel guilty because they never wanted the child. They might have the child but never pay attention to him or her. Then if women didn't want to have and that was the reason they didn't want children then they would have to be d in order to follow the law.