Not sure about Korea, but Japan's case is more interesting than simply adjusting for population: the government strongly incentivizes new buildings every few decades. There is also a culture of viewing housing as a consumable, which is the part that sticks out to me the most.
yeah there is an expectation that you're either building a shrine type building (in that it's gonna be built to last and venerated) that will be there for 300 years, or else you're gonna replace it in <30.
that also leads to a lot of experimentation in architecture, since this building ain't gonna last so get weird. downside is it leads to a prefab corner cutting approach.
my brother lived in japan for a while and he loved it, both the long-standing rural places that were legit old school, but also when he was in the city and sublet some hypermodern, querky places on the cheap.