Outside of the major city cores, much of what China built wasn't "housing" in the sense that most Westerners think of housing. The buildings often looked superficially like housing but were never really usable for that purpose. They were more like physical "tokens" used as speculative trading vehicles. Now some of those are being demolished, either due to lack of consumer demand or because the "tofu dreg" construction quality was so bad that they aren't safe to occupy.

I guess it wasn't housing in the sense that Chinese think of housing either, or more of it would have been occupied.