It's regulations. But before you call them broken, some of it is safety. Safety standards keep rising with technology and the economy as people can afford more. Same with cars. There's also zoning restrictions in some places designed to prevent slums by requiring large residences. I guess that's happening here too.
Also living standards, ancients houses are dead simple and today could probably be built with usd 5k-10k in a couple months. But most people wont accept a home with no electrity, no lights, no AC, no indoor plumming, etc.