It is because we are a nation of immigrants and there are aspects of our culture that we want to maintain. Outside of the US, we are all seen strictly as American. Don't go to Europe and call yourself Irish or to Africa and say you're African. Both places we are only seen as American. Same thing with Latin America. That aside; some of us have had oppressed pasts that we were less than dirt; Africans, Irish, Jews, Italians, Chinese and Native Americans were all on the bottom of the list. As a result, people are proud of their heritage while people who were not oppressed like the English and Germans, don't have this obsession with their heritage.