I'm willing to bet every town with over 500 people in America has a shitty local diner with greasy food for dirt cheap prices, and any town over 10k has at leas

I'm willing to bet every town with over 500 people in America has a shitty local diner with greasy food for dirt cheap prices, and any town over 10k has at least one Denny's, so "why doesn't anyone do what Waffle House does" isn't really the question. The answer to that is "plenty of places do", they're just not chains. But really at that price point and that kind of food, if you really need a chain restaurant, McDonalds is going to fill that niche just fine. The other places are more upmarket, yes, because "greasy food for really cheap prices" is literally McDonalds. Anything between that and a real sit-down-and-order restaurant is called fast casual and you're going to pay a bit more for it.