This is less of an issue in America than it is in Europe, and I think it comes down to religion. The immigrants to the United States are generally more likely to adjust and conform since American culture is highly syncretic, and refugees are more likely to be Christian and meld into the predominantly Christian Unites States.

European immigrants are more likely to be Muslim, which clashes with European customs, cultures, and ideals. This is why they form such tight, insular communities where they can control the communities customs and ideals. You see this in Muslim and Jewish communities in the United States as well but it is less pronounced.