Those places make their way by offering the so-called “comfort foods,” but you can’t extrapolate their clientele to the rest of Americans.
What do you define as “Main Street, USA?” Rockville Pike? Connecticut Avenue? Main Street, Cropdust, Kansas?
My (British) grandmother is worse than most Americans I know. She’s strictly a meat & potatoes eater, years after my grandfather passed on. She wouldn’t even eat my dad’s lasagna until she watched over his shoulder to see exactly what he was putting in.
I’d find a few mexican places sandwiched between occasional thai, malaysian, ethiopian, japanese, american, and countless other restaurants offering every type of cuisine, the majority of which could not be described as “bland”.
I’d have a very hard time building up a sweat walking down any number of main streets without bumping into a place that didn’t serve “bland” cuisine.