That statement is kind of what I mean. I don’t think most people outside, and to some extent inside the US, appreciate how much diversity of culture exists in the US.
Eastern Washington is completely different culturally than western Washington(Seattle etc).
No where else in the world has the massive amount of diversity that the US does at the scale of the US. It’s not even close anywhere else so it is difficult for both US residents and people of other countries to fully comprehend.
I honestly feel as though this is a lack of awareness of other regions and the differences inside of them. I don't know how you can make sweeping statements like that. A cursory look at a linguistic diversity map should immediately hint at a different reality, and that's just one metric. There are places in Africa where you have genetic lines that are distant by tends of thousands of years from surrounding villages as measured by their Y chromosomes.
You ever been in Spain, Italy, Germany or France?
This is simply not true, in Spain they have so many different languages, in the others they have incredibly dialects that seem like entirely different languages and can be only as short as 25km away from one another--something like Badish vs schwabish vs Alemansich vs Hoch Deutsch.
You have to live in places like Hawaii (which I did) before you get anything close to the stark differences I'm talking about, where they have an entirely different set of culture and language (Hawaiian pidgin) to see what is so pervasive all throughout Southern and Central Europe.