The OP is something I've wondered about as well. I'm an expat Australian living in America and it used to strike me as odd that Americans of certain European descent hark back to their distant heritage in ways that used to seem almost far-fetched to me. But ime, defining your ethnicity is front and center in the US. Americans of Asian descent and Latin descent do it to though it may be questioned less because their appearance reflects their heritage more obviously. My ethnicity never goes unremarked upon and I am conscious of being stamped with it here, like it being a descriptor that matters. I can see how that consciousness may be passed down through generations and that the American habit of defining one's ethnicity is like a cultural habit meme. There is also the fact the at one point, someone's forebears were proud of where they came from and wanted to pass a strong identiy on to their children who then passed that on to their own children and so on. Not all that unusual. If I have children, I will most definitely impress my heritage upon them because it's a way for me to still feel like I belong to the culture of the country I was born in.