The root cause is fewer desirable jobs. Fewer businesses with a larger share of the market, in fewer and fewer places.

Desirable jobs is also a moving target. I’d bet a lot of money that virtually every job is safer than in the 70’s, more are indoors, fewer are outside or demand physical labour. If you mean that the supply of desirable jobs has increased slower than demand, sure, I can buy that.

Fewer jobs offer job security and decent pay. Because of less job security, you need to be in a market with many employers (aka cities), and this results in more people living in fewer places, which means higher rent.

That translates to needing higher pay, or at least a career where you can outpace rent and insurance costs. There are some manual labor jobs that pay well outside of cities, but you have to watch out for the condition your body will be in since people live longer and there will be less of a social safety net for when you are disabled and/or are too old to work.

Bottom line is more and more people are less and less valuable.

Japan doesn't have an artificial demand problem like some other countries. They're also not mentally disabled by skin color.