The government of China let developers sell un-built apartments to future residents. The residents not only paid down payments, but took on a mortgage obligation for an un-built building. "The majority of new properties in China — about 90% — are sold before being completed." - CNN. This produced a terrible incentive for developers to do huge numbers of housing starts and then not finish the building.
In most of the rest of the world, developers have to finance construction with their own money or a high-interest construction loan, then sell the completed building. This gives developers a strong incentive to finish the job. Building quality control is often a problem, but unfinished projects less so.