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.
But, the only alternative considered is private individual/family transport.
Why is private mass transport not more widely available given that it can solve a lot of these problems?
Having an Uber for buses which does smart scheduling based on current demand, possibly involving transfers so that frequent local routes connect with each other without long delays, should be possible.
Of course, prices will fall when things scale. So, the government can be involved as a facilitator but operations are mostly run by companies which can pay a fee to the government rent necessary infrastructure.
You still have the problem of higher prices for odd hours/locations but sharing costs ahould make it cheaper than uber.