But living in your own house means you have your own roof, that can just as well needs maintenance, and you also can pick a bad contractor, and so on.

There are trade-offs. And there are external costs. Having your own backyard means usually having and using a car, taking up space close to downtown (because fuck commute times, right?) for just a family (and taking up road capacity too). These are currently undervalued.

The whole housing calamity in the Bay Area (and in London and Berlin) is manifestation of exactly this. (Plus idiotic zoning laws and height restrictions, and of course grafts, bribes, corruption, and the usual.)