The situation is way more complicated, it isn't a simple scam. It certainly didn't start out that way. The developers fully inteded on building these homes (at least until recently). And the business model was sound and generally works.

Pre-selling of units in apartments/condos is common around the world and a key part of securing the cashflow for the project. Chinese developers were operating just as anywhere else. The model is - use internal funding + pre-selling to build the project, then sell the remaining units once done. Use the money from selling the finished units to pay for the next project. Since demand for homes was super high, they started planning the next project before the first one was finished. Same as anywhere else in the world. The issue started that finished projects didn't sell the remaining empty units at the expected rate. Eventually the capital of the development company was mostly used up and the cashflow from finished projects dried up. So they had a lot of half built projects and the only money available was that from projects even further in the future. And that's not sustainable and here we are now.

There are three big factors why the finished units didn't sell.

• Pre-selling is cheaper. So homeowners opted for that. You usually are given a decent discount and have much easier payment terms. You often have a few years of monthly payments before the lump-sum is due. So by the time you need that mortage you already have 10-30% equity in the unit. Making the mortage lower and easier to get. And if your financial situation changed, you can even sell the unit before the lump-sum is due.

• China has rather restrictive rules on owning land. In many muncipialities, and especially in big cities, people are only allowed to own 1 or 2 residential homes (there are ways around it). Foreign entities aren't allowed to own residential properties for investment purposes in general. So unlike in the west where you have a conglomerate of investors buying up all the homes with the plan of making their money back by renting them out, Chinese investors have to rely on people buying their own home for personal use. Which means there is no real option of selling empty units on mass for a lower price.

• The rate of rural to urban migration slowed down. In the past few decades China experienced some of the fastest growth of urbanization ever. Tons of people coming from the countryside to live in the city. This created the illusion of near limitless demand for homes. But now it's very likely that the Chinese government lied about their population. So the demand for homes can't be as high as expected but on top of that, migration to urban areas has slowed down.

Now a lot of these things have been known for years. And nobody really did anything. So I personally think calling all of this a scam is fair at this point. But the Chinese government could step in and help out their population. If these developers really go bankrupt, the government could just seize all of the empty unsold units and redistribute them to people who got fucked over. It isn't perfect but it's better than not having a house. The big question is just, how many of these units are actually habitable. China has questionable building methods to begin with and on top of that many of the buildings were so empty that there was no money to pay for maintainance. So alot of these homes are death traps. And I suppose no home is better than a death trap.