Also, many european cities are build quite dense because of their age. Especially medieval town centers are build dense because building large buildings was very hard to do.

This results in many requirements for living being close together(shops, markets etc).

Also, the automobile made it possible to create large suburbs in america. In many european cities the focus on the car didn't happen because spending money on a car was not a reality for many people. (americans own considerable more cars then most europeans, and have so for decades, even compared to western european countries).