Plus if they moved beyond mom and pop status and somehow kept their costs dramatically low, there's always a bigger company willing to buy them out to protect their spot.

Maybe mom and pop shops can beat them when it comes to black coffee, but I can think of one small place I've ever been to where anything beyond that saves money, it's usually the opposite. Those lattes and shit are not cheap even when the big places can buy the actually valuable ingredients at high scales. And I'm pretty sure that one place that competed was campus subsidized. It was also not good coffee.

Iirc the local place I went to back when I lived nearby sold black coffee at about 70 cents cheaper for a large cup, and being the local place with maybe three employees ever on at a time in a liberal neighborhood, was absolutely packed during any rush time. That 70 cents isn't going to kill Dunkin, their convenience, familiarity, app preorders, bigger menu, often ideal locations for being on the go, etc. I believe the local place near me now is more expensive than dunkin, so it's not even assured that local places can even try that.

There's a demographic of people who want a local place that is cheap and familiar to them, but there's a much, much larger one that wants the convenience of a chain, or if not that a place that specializes in gourmet coffee like a roaster, which also isn't going to be cheap. And if people are super money conscious, they'll make coffee at home, or gas station coffee on the go, which isn't all awful. A coffee place at a cheaper price point than what's out there right now doesn't seem very viable at all.