One reason for that is a general lack of commuting there. You have high gasoline costs. In countries other than Germany, there are no freeways. So if you work in a European city, generally you live in that city. Many U.S. economic policies make things different here.
Gasoline prices are low.
We have a highly developed and funded interstate highway system. After World War II, we provided economic incentives to encourage returning ex-soldiers to have homes built, and with limited space in the cities, many of them built outside city limits, beginning some of that sprawl. We haven t provided many economic incentives for mass transit. The result of all this is that many people live outside the cities. The American love affair with the automobile began at the turn of the century.