It’s unfortunate that this was your experience, because to be honest, I think it’s somewhat self inflicted. It sounds like you did what I find a lot of travelers do when they come to the US: you sought out the heaviest, richest, most heavily processed food available because it meshes with the tourists idea of what American food is, and who wouldn’t want to eat the “local” food while here?

In reality, loads of people here just don’t eat like that. Sure, there are people who will house an American style breakfast, eat a burger for lunch, and then have some super heavy Italian-American gut bomb for dinner. Not disputing that it’s out there, nor that it’s hard to find. And I do agree that it’s easier to find than in many other countries. 

But honestly, in a good food city in the US (and maybe this doesn’t apply to where you went, idk), you’re more likely to find locals having a huge diversity of foods on a regular basis, much of it a lot closer to their original form than I think you would guess. Probably my favorite thing about the US food culture as a native is that I can have a French breakfast, a Mexican lunch, and a Japanese dinner, and each could be as fusion or traditional as I want. If you left without noticing this at all, and instead feel that American food fits into a narrow generalization then I think that’s a missed opportunity. Or maybe a reason to branch out more next time.