The entire world has been doing it for the last decade, and there’s been another uptick recently. The US recently resumed buying treasuries. This is not isolated to China.
https://www.bloomberg.com/news/articles/2019-10-08/powell-sa...
This has nothing to do with ghost cities (which can probably be blamed on bad central planning and an overheated property market in China).
Plenty of houses in Detroit
Why 50 Million Chinese Homes are Empty - https://www.youtube.com/watch?v=f5SE47Xjx2Q&t=2s
I love California, and would like housing there.