People moved out to the suburbs for a lot of reasons--not least of which was the post-war baby boom. The US government certainly didn't discourage it (though they were arguably pursuing policies the majority of the population wanted) and the exodus added fire to a self-reinforcing cycle of urban problems (including race-related ones)which lasted at least through the 1980s. And arguably we could see movement out of at least some cities again.

I'm not especially pro-suburbia--I live in an exurban/almost rural location. But I think it's perfectly understandable why many people wouldn't live in a city given a choice which they increasing had post-WWII in the US.