Americans own cars because most of them live in single-family houses on large plots of land, and that doesn't make public transit for daily commuting a realistic possibility. In Paris car ownership is very low, maybe 1/3 of adults, but in rural France the car ownership rate is easily 95%+. I haven't seen a single developed area in the world that has violated the rule that low density = high car ownership and vice versa.
The other rule that I have never seen violated is that the large majority of middle and upper income people do not want to live near low income people, due to crime or other reasons. In Europe, poor people live in the suburbs, so the middle income live in the city with high density housing. In the US and some other places (south asia), low income people live near the business center, so the middle income live in low density housing in the suburbs. These are for historical reasons and cannot be easily changed.
The real reason Americans own cars is because we’re rich enough to afford a more expensive and more convenient system. Public Transit at scale is surprisingly cheap when compared to all the costs associated with car ownership * 10’s of thousands of people in even a fairly small community.
I now live in the Seattle suburbs, Redmond — very close to the same distance from the work site as in Copenhagen — and there is no way I could realistically rely on public transit to hit appointments unless I left an hour or two early—and, in bad weather, many hours early. I can’t imagine doing what I do without a car.
I’ve done long commutes and I’ve lived close enough to walk to work. If I and millions of other people had prioritized car free lives 20 years ago we would already had noticeably different infrastructure. Instead I’m back to “needing” a car to get around based on these kinds of choices.