The other poster is certainly right about the complexity, but to give some minor bit of insight into the issue:

1) Renters in China have very little legal protection.

2) Expectation in rural communities in China is that a male suitor should have a house before marriage. Male suitor’s parents pay a good portion, and indirectly so do his sisters (in that another expectation in these communities is paying a bride price, despite it being illegal, so basically the sister fetched a bride price that helps the brother pay for his bride). Old traditions and the gender imbalance seem to have contributed to all this (many guys won’t be able to find brides, and some will pay human traffickers who kidnap Chinese women from the cities or use fraud to get wives from viatnam and other such poorer countries).

3) In wealthier circles in the cities providing a house seems to have become something parents of children of both genders have started doing. I don’t know whether it is an extension of the traditions noted above, or maybe stronger beliefs that parents should set their children up in life (and in turn expect support later)

4) The Chinese housing market has done so well for so long people expect it will continue. Meanwhile, the stock market is regarded as gambling, and given the level of insider trading that can somewhat be understood.

I’m sure I’m missing a lot of things, but there’s a quick attempt at an explanation.