Walking is, I think, a combination of habit and culture. Both sets of my grandparents, from opposite ends of the country, used to walk quite a lot without any real purpose for doing so. They did this well into their 80s, and so did their friends. It seemed just to be something they did, and always had done. My parents, by contrast, almost never walk when they can drive, and will often drive to a park to let their dog…
I think location is also a big factor here. I've lived in multiple parts of the US, and most of it is simply designed against walking. I enjoy taking casual walks, but when I lived in the midwest, I had to drive to a park to walk. There were no sidewalks, and the streets were dangerous for pedestrians (lots of blind curves, speeding cars, etc). It always frustrated me that I had to take a vehicle to go for a walk.
Some places are actively hostile to walkers: building only arterial roads and refusing to build sidewalks to exclude walkers and the wrong sort of people (black or poor). Relatively few places are so hostile to drivers. So people grow a bias toward driving everywhere. Load your bicycle on the car and drive it there to ride around in circles.