But stay in the office for 80 hours a week even if you aren't productive. Also you are paid only enough to afford a 1 bedroom apartment because there are too many people and not enough homes.
There's a plateauing effect that's been observed when health, happiness, and comfort are reached within a country. When your country doesn't have a high infant/child mortality rate, you don't need to have more than 2-3 kids. So the birthrate tends to go down.
Japan is sort of a whole different beast. There's some pretty good documentaries that discuss the issues when observed from certain fronts: the grind culture, lack of childcare, lack of gender equality.
There's a lot of cultural things that need to be fixed in Japan, and no one wants to change.
That's true for most of the developed world though. And honestly that's what's actually required because the planet can't sustain this level of consumption from this many people so the population actually does need to go down.