This is the main issue. There’s not enough skilled workers to actually make enough houses and homebuilding supplies. It’s so expensive and the average person can’t do it up to code.
Before, if you had some small amount of money and a lot of time you could just buy a small plot and build a house yourself. Now you’d be an idiot to waste time doing that. No one will buy your handmade house even if it’s up to code.
Apartments in cities used to be cheap because the city stank of horse manure and smoke, and there were no elevators. Basically we’ve made the world much nicer and realized people will pay an arm and a leg for a nice place to live.