"some time right after WWII, people in US suddenly decided to live in a poorly built and ugly looking dwellings regardless of their income level. "
We stopped living in walkable villages and cities and started living in motorway dependant sprawling suburbs. Our buildings got uglier. Our built environment got worse even as we got richer.
Largely this was a matter of public policy. The Roosevelt administration made new rules to plan new development to promote industry during the Depression and imposed it on banks and local planning boards. Still, there wasn't enough push to get the banks to allow anything to be built. Then after the war, those regulations had been in place for almost fifteen years and nothing had been built in the whole country for 16 years since the Depression began.
So people took the rules as gospel and built using them. The only thing allowed was car dependant sprawl and the car companies -- an enormous political power right after the war -- loved it. So the whole country was redesigned. It still is. And if your community isn't worth loving -- as sprawl isn't -- then it isn't worth building beautiful buildings.
That's why this is now the nation of NIMBYism. People can see that nothing has gotten built here but garbage since 1929 and they don't want more of it. Places like San Francisco are now like jewels and museums since nobody has been allowed to build like that in 86 years and won't be allowed to start tomorrow. The epoch when things could be new and beautiful has passed from living memory.