It’s an odd thing, really. I’m not sure if it’s uniquely American, but maybe because their ethnic identities and national identities have never been 1:1 at any point, it’s easier to map and identity onto something else. Americans do have a keen sense of immigrant identity, whether materially real or stolen valor, even those who have assimilated completely into American culture. Many large immigrant groups lived as close to the exact same as they did in Italy, Ireland, Germany, Nordics, etc as was possible, so modern Americans seem to idealise family heritage as an ethnic identity in and of itself.

Just spit balling, but that identity probably wraps into the American dream subconsciously. That the family didn’t have any when they arrived, and now they have everything (a Ford F150).