The US population never got to unify as one people with a common culture, so they identify with their DNA to have something similar to what most people in the world has, a place, a culture and millennia of history you are an ingrained part of. There was political will to try uniting the population in the first half of the 1900’s, but their racial focus kinda was a fork in the road for that whole project.

So while the rest of us see them as solely US-ians, we have to suffer through the “I’m 3,17 % Bohemian” bullshit. And it is really stupid, but I do understand where it comes from.