One thing you must consider is that Doo-Wop was mostly sung a capella, or at least with minimal instrumentals, and then only added later in the recording studio. There is a strong Italian tradition that exists to this day in Italy for singing a capella in the streets of Italy as a form of entertainment. I think this tradition was one that was easy for Italian-Americans to adopt here in America. Singing acapella, as a result, was quite natural for Italian-American groups in New York and other cities on the east coast. This tradition of a cappella, which means in the style of the church, probably was not shared by other ethnic groups. Hence the disparity between Italian-Americans and Jews, Irish, and other ethnic groups living in big cities,