If your great grandparents came over from England or Ireland

If your great grandparents came over from England or Ireland, you’re considered either white, or Anglo-American/Irish American. But most people just refer to you as white or American. If a Slavic person moves to the US, their grandchildren aren’t considered Slavic Americans, just American. There’s no way to tell apart an American of Slavic heritage from an American of English or Irish heritage. If an Italian moves to America, their grandchildren who may still look Italian, Sicilian, etc. are usually considered just American or some people might call them Italian because those phenotypical traits are still dominant. Why is it that Slavic people are called Slavic until they arrive here and their children become fully Americanized?