China building unoccupied cities has more to do with the fact that the average Chinese citizen is not allowed to speculate or invest in much other than real-estate.
They failed in that there was a huge investment to build them, but the expectations for these cities were never met. Additionally, there is tremendous upkeep or maintenance.
For example, those new roads are crumbling and require extensive repair work. Think of a road that is 5 lanes wide, but a 1 lane would suffice to serve all of the traffic. The unused portion will still degrade, even though it's not used.
It's kinda like buying a huge house before having children. You still need to fix, maintain and clean the extra square footage, even though it's not used.