Haven't they?

I think our housing shortage would be less if we forced apartment owners to report the number of apartments they are holding off the market. But they won't because that would then force rents lower if we truly had a market economy instead of an oligarch economy.

that they can't afford to finish for several reasons, not the least of which is that a finished unit sells for less than an unfinished one due to a peculiarity of Chinese culture. They can't afford to finish them out for themselves. Most of them don't have roughed in plumbing or wiring as we understand it, it all comes out of one box and must be connected there and then roughed in, another expense. In addition, the "ownership" is of a 70 year lease, not outright ownership. That's a generous assessment of the useful life of those hastily slapped up high rises, in any case.

So the Chinese have temporary ownership of unlivable spaces and that has done nothing for the housing crunch.

As an aside, I read an interesting (if true) factoid in the last couple of weeks, that thanks to the building bust and fallout from the misguided zero Covid policy, something 25% of men 18-34 are now unemployed. That is a lot more serious than unfinished buildings and inconvenienced billionaires and Xi had better address that one first or he's in trouble.