it’s illegal to build more of them in almost all places in the US. San Jose, a city of over 1M people, was zoned 96% SFH until like 5 years ago.

So prices do existing ones are high. Labor is taxed heavily compared to rental income so it’s a slog to break into the capitalist class. This wasn’t the case 50 years ago though, because we let people built apartment buildings then. So plenty of people could buy in at that time.