They're there, just not where you were I guess. I've seen Indian places in rural Missouri. Tibetan in rural Maine. Vietnamese and Filipino in rural Georgia.
People of all nationalities are scattered throughout the US and have opened restaurants with varying degrees of fidelity to their origins in many cities and towns.
They're usually out there but so few people know where to look or bother to do so that it's pretty frequent that white American families just end up at some chain resturant instead of noticing the little Thai place around the corner.
I grew up in a census designated place and there were plenty around where I was. It wasn't a super low density region or anything and a city of a few hundred thousand people was maybe a 15 minute drive. But I can't agree stronger that it isn't like you have to be in SF or NYC to get exposed to cuisines from other countries.
People of all nationalities are scattered throughout the US and have opened restaurants with varying degrees of fidelity to their origins in many cities and towns.