It's the same situation as described in my comment. You have a robustly growing market so it attracts investors and then speculators, especially if money is ch

It's the same situation as described in my comment. You have a robustly growing market so it attracts investors and then speculators, especially if money is cheap. This drives increase in supply but that lead to a bubble. For instance, new builds can be snatched by speculators even if they remain empty because market value increases 10% year on year so who cares... until something happens and the bubble pops. Again, this is a common pattern in growing markets. People might also try to sell to avoid repossession if rate hikes make mortgages no longer affordable.