Exactly my experience. I've been to a lot of McDonald's everywhere from rural to old inner city, and the difference is Stark. The more rural locations tend to be clean and relatively comfortable and enjoyable to be in. The inner city locations tend to be dirty, crowded, and generally not very pleasant to be in.

And it's not just McDonald's, as you mentioned. I've observed the exact same thing with Wendy's and many other restaurants as well.

There are of course plenty of exceptions. It's perfectly possible to find a dirty uncomfortable restaurant in a rural area, and it's also not difficult to find a nice comfortable place in the inner city. But generally speaking the above is what I have observed most