But it's not just down to city size. Take a city like Provo in Utah. It's not large by any standard, but it's completely designed for cars. It has awful public transport, a grid 'motorway' system cris-crossing it, everything-as-a-drive-thru, lots of unused space, lots of parking lots... If you try walking around it, you'll just spend hours walking past nothing in particular to get to nowhere special.
It isn't surprising that so many cars are on the road when just to cross the street you need to walk a quarter mile on average. Then you have to cross the death trap parking lots with zero shade and 120 degree black top.
I've been in the US once, 13 years ago, and it was pretty shocking for me to experience the concept of "car centric" in its full glory for the first time. I was at CES in Las Vegas and went to some club one evening with a friend. At some point I left and wanted to walk to the Hotel alone in order to calm down and enjoy the nice climate. Turned out, there was simply no walkable connection between the 2 locations. I couldn't believe it, but - being stubborn - walked anyway, in the dirt along some highway, a bit scared of being picked up by the police, not even sure if walking there was even legal.
Later that week I moved to LA and first saw the endless suburbs of an American city, from the air.
I don't know how representative those 2 places are for the US, but having seen that, I can totally understand why many Americans have a very hard time imagining life without a car.