Because a large portion of the population has a vested interest in not having more housing. Not just the rich. But the upper middle/middle class nimbys as well.

There’s related issues, fixing both together is the most efficient path. Turn parking lots into housing. Take garages out of plots and you have another spot for a house. But people don’t want increased density. People need to have room to not have a car if you want to increase density to better levels.