Cities may have become denser but cities in the developed world became far nicer places now than they were in 1945. Plenty of rich people live in city's not becase they need to but becase they like it there. What changed was not the removal of people from cities but industry from cities. There are plenty of great things about being near other people, and plenty of horrible things about being near industry. Indoor plumbing and the catalitic converters changed what people think of a city's that only contain people from toxic dumps to livable space.