It's difficult to enforce the two kid policy. A lot of better-off countries were doing so without really knowing it as educated people seem to breed less, but with the amount of immigration and refugee movement lately there is a turn of events where formerly poor people are now witnessing an abundance and breeding like jackrabbits as they did where they came from. This creates a situation. Mortality rates are much lower in wealthy countries, so this leaves many more living relatives of refugees and immigrants from poorer countries. The refugees and immigrants of days gone by didn't see much of a difference, or even a slight rise in mortality upon reaching a new country (talking about North America here) as they were not subject to abundances of food and shelter; rather they had to break ground on a new farm or create a business and start from the bottom. They continued to breed as if they were going to lose a few kids and gradually plateaued to a median. In the 1950s and 60s you could see Catholic, formerly farm people still spitting out 8-10 kids pretty regularly, yet they lived in a city. That stopped within a generation, but the mentality came from the farms and religious structures based on not counting your chickens before they hatched.

We're also on the cusp of three giant, formerly-third world countries reaching an economy of status. The breeding is still happening as if mortality is expected, yet the money is starting to come in. The technology made available to these parts of the world also makes mortality rates drop and there we have it, lots and lots of people!

Just saying what I'm thinking. This is in no way researched.