An American from Idaho will be able to communicate, trade and watch the same tv as someone in Vermont, whereas a person from Malawi will not be able to do any of these things with a person in Guinea
In comparison all of Scandinavia has a similar population size as the New York metropolitan area.
Instead, there are regional supermarket chains, some of which branch out a little into areas where they are not the dominant store.
Examples:
Albertsons: mostly in the western states
HEB: Texas only
Publix: southern states (all the way down to Key West)
Piggly Wiggly: hard to describe, but mostly a stripe running up through the midwest
Fairway: NYC, NJ and almost nowhere else
Now, had you written that about, say drug stores, it would be more true. Everywhere you go it will either be a CVS, Rite Aid or Walgreens. There are independents, but these 3 dominate the entire country, with some regional focus, but always a national reach.
Of course you can find McDonalds everywhere but you’ll find those in Europe, also.
I think the main thing that makes it feel superficially homogeneous is the shared language - which is now even more shared since the advent of Hollywood and national entertainment.