Most Americans need cars.

America is a vast land compared to European countries. Public transportation can only go so far. Some American suburbs stretch more than 80 miles out of major urban centers.

Most Americans need cars because American urban planning has been for many decades built around cars.

This, of course, is a solvable problem.

(It has nothing to be with how big the US is, it has to do with how US communities are deliberately engineered.)

Solvable by what? Demolishing the suburbs? Building new cities in the middle of nowhere? A time machine?

Some improvement can come from just improved planning in the cities we already have. Relaxed zoning for density, exclusive corridors for mass transit, etc.

Definitely. Many suburbs need to return to farmland, we have paved over most of our prime farmland for shitty, rent seeking suburbs.

Dense cities are cheaper to live in, cost less to maintain for everyone involved, and give people back time that is currently stolen from them during the average commute. You also end up with better infrastructure, lower taxes, and usually a healthier and happier population in dense cities.

Suburban and exurban slum development with 1 to 3 stories and a 1 to 2 hour commute is destined to die, its just a matter of how and when. Detroit is one failure mode, while Livingston, TX is another (tax base could never support the infrastructure built), though the latter case is very common.

Everyday people commute from all over England to London, via train.

...because the marketing department tells them they do?

It's certainly a factor, but I think claiming that is the only factor is an oversimplification.