My (simplified) understanding is that it's more about the ideals. Back in the day, part of the American dream was to live in a semi-secluded suburban neighborhood and own 2+ cars per family. Only the poor and young people were expected to live in city centers. Therefore, the affluent citizens spread out, and cities evolved to cater to their needs, i.e., support private cars and the road system at the cost of not properly funding public transportation. In European cities the ideal was the opposite, and it was thought that only peasants would stay secluded and all the affluent people should live in the cities, which in turn should have great public transportation for practical reasons. I'd imagine that ideal extended to Canadian and Australian cities as well.