It’s not just “us” who built cities to maximize car travel. Everyone did it. Walkable european cities are surrounded by car-dependent suburbs.

The problem with your analysis is that your concept of “useful” is based on a set of priorities in your head that’s almost certainly not shared by the people who prefer to live in car-optimized areas. Cars let you travel in private, on your own schedule, without having to interact with other people. You might not value those things. Lots of people do.

I'm not convinced that suburbs outside the US are quite as hard to walk in as in the US.

Just about every UK suburb is walkable to train station a supermarket some smaller shops and probably a pub somewhere.

I the US the sidewalk just ends and walking can be quite dangerous in places.