This is a similar question to what percentage of people use all those empty condo-cities being built in China. The answer is: a perhaps-negligible number now (except around existing metropolitan centres, where there's respectable usage), but with projected growth toward capacity as GDP rises.
Because Chinese civil-planning policy isn't a matter of election promises, it isn't constrained to showing benefits within four-year periods. A lot of the things China is doing don't "make sense" from an intuitive standpoint if you're imagining anyone expected short-term gains, but do make sense if you imagine they were planning for 10 or 20 years down the line.
Those empty condos are unmarketable. As people become wealthier, they're going to change tastes. Even the middle class is going to seek out individual single family homes, instead of the concrete jungle of repetitive jail cells that are those new condos.
They're the poor mans idea of what the middle class wants.
A lot of those cities have the apartments built and sold before they put in commercial areas and most importantly things like subways. There was an episode of Sinica where a guest was talking to a person that bought one of the ghost apartments but wasn't living in it because there wasn't a subway line. The guest went back to the area once the subway opened and most of the apartments were full and roads were being used. I think it was this episode[0] but not 100% sure. I know the section I'm talking about was towards the end of the episode.
Because Chinese civil-planning policy isn't a matter of election promises, it isn't constrained to showing benefits within four-year periods. A lot of the things China is doing don't "make sense" from an intuitive standpoint if you're imagining anyone expected short-term gains, but do make sense if you imagine they were planning for 10 or 20 years down the line.