There really aren't, proportionally. Most of the cities are not reasonable to live in without owning a car.

And I'd rather if the bus was an option at all. The bus is expensive and unreliable in most US cities. Getting somewhere by car that takes 20 minutes can take hours by bus due to scheduling. This is a stark contrast to London, which has an actual public transit system.

Maybe I'm biased by living in Colorado Springs, where it might be particularly bad, but cities with sprawling suburbs are usually terrible for living without a car, and the US has tons of suburbs.