I've never eaten marshmallow fluff.
and the last time I had marshmallows involved a campfire longer ago than I can remember. (unless you count Peeps, because I did eat a few of those last Easter during the great Peeps massacre of 2016)
Also, in addition to the whole based on gas stations/convenience stores rather than actual grocery stores, there's also a lot of general food that I imagine is the same from country to country and won't be specifically in the "American" section or sorted by items rather than country.
Most grocery stores I go in that have sections dedicated to "ethnic" food generally have some overlap in other sections or the "ethnic" is group based on a primary item (like Italian gets in with general pasta which also is where the raman noodles are, boxed food like Hamburger Helper overlaps with taco kits, which leads to the Mexican food and on and on) while the aisle that does really specific "THIS IS ETHNIC FOODZ!!!1!" will only have imported items and such.