But it doesn't have to be that way. I'm in Munich now, and little Bavarian towns of 10k or less are nearly always much more walkable than US cities 20x their size.
But for day to day errands, you don't need a car, you can get by fine without one. That's the difference. You have a choice, whereas in the states you don't. Small towns in the US are mostly hilariously walking-hostile, and public transportation is effectively non-existent.
I admit, it's a bit amusing to see how often Americans treat this as something that must be either-or. When I talk about German cities being more walkable, or having public transit, so many assume that this means driving is either impossible or impractical, as if it was not feasible to support more than one mode at a time.
Though I suppose I can't really blame them, because that's more or less how things work back in the states: most cities are designed for cars to the near-exclusion of all else. You can walk, but there's nothing in walking distance from the residential areas. You can bike, but it's dangerous and uncomfortable. You can take a bus, if you're okay with tripling how long every errand takes.
A lot of cultures you go up to the grocery store to buy what you need for what you're cooking that day. Not going once a month to fill a truckload of year long supplies.