You are absolutely right.

I think this is a question that is most easily answered by non-Americans who have visited the country. Mostly because we have a certain perspective that lets us see things others might overlook.

There's multiple "American" cultures.

I've visited multiple cities across the USA, and each place I've been is insanely different. Different accents, different values, different food, and different music. Hell, just the food should be enough. The BBQ in South Carolina, clam chowder in Maine, sourdough in San Francisco, pizza in New York, pizza in Chicago (a wholly different beast, but still delicious) - and holy shit, Portland beer is awesome. Nothing washes down a spicy bowl of Louisiana gumbo better than a bottle of Portland beer.

That's something I really admire about America. You've taken all these people from different parts of the world, and each one brings a little flavour from home. Hell, New York is the only place in the world where I could get food from literally every country I've ever visited. Practically within walking distance from my hotel. Do you have any idea how amazeballs that is? A 5 minute walk, and I could have shawarma in one hand and schnitzel in the other (and both would be at least 10% rat hair, but that's a different matter entirely).

I'm not even touching on American mythology, like Paul Bunyan, Johnny Appleseed, and Davy Crockett. Or your music, like bluegrass, jazz, or rock'n roll.

Unfortunately, this has confused many of your fellow Americans that not having a singular culture is the same as having no culture. They then take their confusion & ignorance and project it onto the entire world.

As far as they're concerned, Europe is basically generic, interchangeable white people. This is because their exposure to other cultures is so limited that they've fooled themselves into thinking that skin colour is what makes a culture. They make exceptions for Germany, of course, because Nazis.