Urban geography: In 1947, the US started to build very low density, cheap, mass produced suburbs. Along with this, most American cities have very little mixed use zoning, and large parking requirements, both of which increase the typical distance a person would have to travel to live a normal life, and make each theoretical train station/bus stop less economically sensible. When in Spain you might have many tens of thousands of residents within a 1 km radius of a subway line, you will not not get one thousand in a deep suburb. Therefore, for the same total population, a US public transit system (outside of NYC, and maybe Chicago) is going to be far worse than the equivalent on most European cities.
This is self perpetuating: Changes in urban planning that would allow most homes in the US to be good residences without a car would involve not just demolishing most cities and starting over. This isn't even just about demolishing suburbs: Even downtowns are built in ways that optimized for the car. Go to your favorite mapping app, and look at, say, St Louis. You will find many buildings are just parking lots, very few storefronts, very wide streets designed to be driven at 60 km/h, and with very few pedestrian crossings... All the infrastructure that makes it easy for most workers to live 20-30 of wherever they work just makes building a useful public transport system unfeasible for a city, and even more so when most voters would be unable to use it.
The same problem is there in small cities, and even villages. A small town in Italy that lives from summer tourism is going to be easy to deal with even without using public transport, and just walking. The American equivalent is unmanageable without a car.
Those that want to avoid driving in the US end up either paying people to drive for them all the time, or live in the pedestrian friendly parts of a handful of cities. And if you haven't visited the US, you probably also haven't seen how expensive is to live in those areas. So, if anything, it's much easier to live without a car if you are a pretty wealthy tech worker than if you are a server at a restaurant, or work at a retailer. The less your job pays, the harder it is to not drive a car.
Imagine a couple of a bank teller and an insurance agent. If they need to move to Madrid, it's very likely that they will find living arrangements where it's easier to go to work via public transport, as most places do. If you do the equivalent in Houston TX, it's almost guaranteed one of them will have to drive to live a comfortable life, and most likely both.