The reality is that in so many countries is that it is too expensive to have more kids than 1 or 2. You have both parents working, living in an expensive place, paying for day care, buying a bigger car, etc.. you end up needing to be well above middle class to actually afford 3-4 kids.. then when you factor in university, then you basically need to win the lottery or your kids end up with tons of debt. And in many cities in China you effectively are an immigrant in your own country trying to become a resident where you can access the cities better healthcare system and schools etc.. so people have a big incentive to want to live in the bigger more expensive cities. (Which ends up making it more likely people will have fewer kids)