They don't. Larger cities have many loops of busy highway belts embracing the city, and plenty of tunnels, parking lots and emissions (ie Madrid, Rome, Paris...). But there's always a sizeable walkable urban area, usually proportional to the overall city-size. Even Stuttgart has a nice downtown walking area [1] and a usable public transport system [2].

But, as a fun notice, Stuttgart could be somewhat of a "Detroit of Europe", being the home of Porsche and Mercedes-Benz, so there's added incentive, and pride, to be a car city.

[1] https://maps.app.goo.gl/aQCEYkc3oWsKpD9F7

[2] https://www.travelstuttgart.com/transport-in-stuttgart.html