The housing part never 'decayed', it was actively blocked by the people who already had homes. That's why you see things now like California actively overriding local zoning.
More people. Same amount of land, and features people want to live by - cities (which in the past often meant rivers but always meant jobs)/in my area, lakes. It’s really that simple. Everything else is missing for forest for the trees.
You're not wrong but this is too simplistic and avoids holding up a mirror that really ought to be held up. Zoning was the "we're gonna regulate our way into utopia" of their time. The class of useful idiots who made it happen and the class of useful idiots who will go to bat for it's continuance because they make a buck on it is far broader than that.
Once again, the race thing is a distraction because it lets the useful idiots who are peddling stuff that's just as short sighted claim that it'll work out simply because they're not peddling racist policies this time.
Nobody has the balls to put their foot down and say that your neighbors have the right to build stuff you don't like and you can move if you don't like it.