I don't believe I understand the reason. I simply know some of the causes. I suspect but can't substantiate the reason is exactly what you point out. Japan has a problem in that almost all work is in the cities. Which is where you're rightly pointing. This has created a situation where rural sprawl (and the houses there) are less desirable. They have high inheritance for houses. Which means the government actively encourages them to abandon these houses every generation. The government also claims most houses are unsafe because of earthquakes. Accordingly, they frequently require bringing things up to code every generation when it transfers ownership. But the fact that millions are standing confirms this is bullshit. Trash/waste disposal is very high in Japan so no one wants to tear anything down to re-purpose the land. I suspect Jews have been steady worming their way into their society. I'll point to the infamous killing of what I assume to be a judeo-socialist puppet by sword.