Plus, this is a country made up of a little piece of every other country in the world. "American identity" is an ex post facto rationalization. Not to mention that politically we often operate like 50 small-to-medium sized countries. And there's less of a push to homogenize the country since one of our political parties fights against federalization.
All that adds up to a country with a whole lot of variation. Describing what Americans are like is pretty useless. We're like everything.