> A population of 10 million singles demand 4 times more "housing units" than a population of 10 million people in 4-person families.

Those housing units are not interchangeable. Families often want extra bedrooms, and units with extra bedrooms are frequently sorely lacking.

This is one thing that is very strikingly different in different markets. A lot of US metros have a fair amount of new housing but almost none with even two bedrooms per unit, let alone three. In a place like Taiwan, there are similarly absurd housing prices, but the new dense developments have four- and five-bedroom units.