>>512427233 (OP)
I think it's deliberate, if everyone lives to around 75-80 years old and has 1 child you're over the replacement rate significantly. China, Korea, and Japan basically have no labor unions, so they're stingy about who gets trained in essential jobs. Often they'll just outsource maintenance jobs to foreigners on visas to prevent people from unionizing. So there's 0 incentive for a population boom unless they create a self-sufficient population. All 3 of those countries aren't self-sufficient in both food and energy, they do this deliberately to keep social order and basically have their schools exist solely as academic drills emphasizing rote memory trivia. A population boom would be almost entirely negative for the systems they have currency, it provides them 0 value and they're altogether unwilling to correct the dependencies they have for the sake of harmony. This is happening in the west too, people who live in glass houses shouldn't throw stones.