Have you been to Indianapolis?
[0]: https://walkingtheworld.substack.com/p/walking-america-part-...
You have a point about needing a car in any number of such smaller cities in America, but even in those places there is a central core that remains relatively walkable.
They're often pretty small though. I'm not familiar with Indianapolis specifically, but there's one smaller city I visit semi-regularly for work. It has a nice (relatively gentrified) downtown but it's, to be generous, maybe 15 x 10 blocks. And beyond that you mostly need a car. I'll have a day to kill there in a month or so and I'll probably end up renting a car for the day.
I also worked downtown of a similar city about a decade ago. Same thing. (And both old mill towns.)