The country's population fundamentals are part of all that too. For housing developers, there's every incentive to choose to build pricey houses because there are still plenty of people buying them.

I saw this recently in a city in the south. Dozens of recently built (<20 years old) developments, each with a hundred or so houses...and none of them affordable on an average income, because there were always plenty of above-average earners ready to buy them.