The cities in America grow because there's various incentives for them to do so, and nothing really constraining that growth in a way that favors cars.

Don't build new roads to the core, maybe even take out, restrict, or slap huge tolls on the existing roads, and you'll keep people from wanting to commute in by car. Also remove rules requiring parking spaces, and even encourage replacing parking lots with buildings or parks or anything else, to make car driving the most miserable experience it can possibly be

There's lots a government can do to make people stop driving cars so much, and stop moving out to the suburbs. There just isn't political will (in America) to do so.