I think you touched on why. Ethnic identity is somewhat arbitrary, and tied up with national / cultural identity. In the US, despite our xenophobic phases most of us culturally identify as a nation of immigrants. So in terms of ethnicity, we’re more concerned with where our lineage existed before arriving in the United States, rather than how long it’s existed in the United States. There’s a bit of a hierarchy of “who’s family has existed in the US the longest”, but all of those claims are still anchored by which nations their ancestors came from.
There’s also the fact that American genetics haven’t been sedentary long enough - And probably never will be - For us to mix evenly enough to develop a unified physical appearance. Ethnicity is of course not just skin deep, but ethnic identity and identification often uses it as shorthand, and there is as far as I know no stereotypical American ethnic appearance.
I think you touched on why. Ethnic identity is somewhat arbitrary, and tied up with national / cultural identity. In the US, despite our xenophobic phases most of us culturally identify as a nation of immigrants. So in terms of ethnicity, we’re more concerned with where our lineage existed before arriving in the United States, rather than how long it’s existed in the United States. There’s a bit of a hierarchy of “who’s family has existed in the US the longest”, but all of those claims are still anchored by which nations their ancestors came from.
There’s also the fact that American genetics haven’t been sedentary long enough - And probably never will be - For us to mix evenly enough to develop a unified physical appearance. Ethnicity is of course not just skin deep, but ethnic identity and identification often uses it as shorthand, and there is as far as I know no stereotypical American ethnic appearance.