Because we've spent the last 50 years with housing inflation above wage inflation and compound interest is the most powerful force. Tax burden has moved ever more to the working classes and away from the wealthy. So we're making less and the price has gone up.

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.

No money for down payment. Mortgage on the median home would also be another 3-4 grand a month. Hardly any inventory much below the median as usually that is just offered for rent.