That really isn't true. Kangbashi (a district of Ordos in Inner Mongolia) is still pretty empty for the amount of infrastructure they've built. They "lowered" their population target and claimed success, and are trying to get people to move there by putting in a good school, but you can still go there to see empty boulevards.

Likewise, China's tallest building is an incomplete skyscraper in Tianjin that hasn't had any work done on it since 2015. Tianjin also overbuilt on a new financial district that no one is really interested in.

Many of these overbuilt buildings are never going to be lived in before they are torn down. They just aren't in very convenient locations (e.g. not enough jobs to sustain those areas and no one wants to commute in traffic to where their are jobs).