Sprawl was caused by the nuclear arms race

This; and it's also the fact that individual houses almost always have basements in US (not the case in majority of the world). They provide for good fallout shelters.

That exploited Soviet economic weakness as well as sociopolitical limitations in the best way possible: the Soviets understood very well what the Americans were doing but they had no way of replying in kind - their feeble economy could not provide a car for every family and even if they could, that will have broken the spirit of collectivism giving people too much individual freedom, endangering their faith in Communism.

Plus of course, building individual houses for every family was out of the question - back then, most still lived in communal apartments and 5-story blocks with 500 sq ft apartments launched by Khruschev and carrying his name to this day, were a prized rarity available for the few. And psychology of centralisation innate for Communists necessitated that the "best", most elite people - highly qualified workers, Party officials, KGB men and the like - had to live in city centers. In America by 1970s, it was the reverse - city centers were left for those... who racists considered expendable.