"America" doesn't consist of LA, NYC, and SF. There are a lot of people even in those places that don't want density but choose the environment because there are jobs, and there are jobs because so few people are willing to leave. (catch 22)
In fact, if we generously estimate that 10 million people live in high density metro areas that don't rely on cars we are looking at less than 3% of the US population. I think that is something to sneeze at.
I know it's hard for you to believe, but some people like living in high density areas.
SF only has a population of one million.
Basically the US has NYC and parts of Chicago as emblems of urban density.