Assuming there's one within walking distance for the kid.

Why wouldn't there be one within walking distance, or even driving distance (assuming most people would want to drive their kids to nourishing activities)?

You must live in a wealthy place.

In my experience in most places libraries are not common. They use lots of space and money, that usually is needed for more important things like building sewers in neighborhoods that have none.

I live in the US, in the Midwest. However it seems that the average distance to a library across the country is around 2-5 miles.

While probably too far to walk for the average American, it's certainly not too far as to be unreachable.

That's fair, but if you have a library card and the Libby app, you can queue and borrow e-books for free and without leaving the house or remembering returns. My kids borrow from their school library but also read on Libby a reasonable amount. I use the Books app. My wife reads on Libby as much as she reads physical books. If we go away for a week, it's easier to pack an old phone or Kindle than a stack of books when the older kids can get through 2-3 novels a day.