I always figured it was kind of a big FU to the aristocracies of the rest of the world. Let's face facts, Americans have always been looked down on by certain elements of the rest of the world. We're like mutts in their eyes. We're a nation made from the cast offs and unwanted elements of the rest of the world and there's always been a kind of snobbishness toward Americans in the rest of the world. It doesn't help that we became an Empire. It's gotta rankle when a people you deem inferior surpass you (economically, militarily, etc) Isn't that part of the problem with white supremacy here in America? Women and minorities, when given equitable opportunity, are surpassing white men.

I digress.

The point is, back in the day, part of becoming American and leaving behind European identities was to focus on America. It was also necessary to leave behind all those bickering past relationships necessary to keep cohesion in a newly formed country.

I don't think most people in the rest of the world get how hard it is to keep any kind of cohesion in a multi-cultural society. Especially one with distinct regional cultures and people from everywhere else in the world maintaining so much of their own mother cultures.

At this point, it's probably mostly habit. There's probably something to being an empire attached to it as well, as it was with the Roman empire.