I think its just white Americans with that problem, other groups seem to have an identity. Why don't white Americans seem to have a culture? I think its an interesting question, I have various ideas, but nothing compelling.
Because white is an amalgamation of many different European cultures (Scottish,Irish,English,German...) that I think all diluted one another to the point that there is no specific culture piece that is universally white-american.
There used to be Little Italy and German parts of town and such, but they disappeared with suburban white flight.