One reason the Italian mob came to dominate, over say, the Jewish mob, is that Italian crime families were multi-generational. Italian-American mobsters brought either their children, nephews, or godchildren into the fold. This was in part because of the structure of organized crime back in the Mezzogiorno. Jewish gangsters, on the other hand, came into organized crime in America and they made sure their children went legitimate. There were exceptions. Hence most Jewish gangsters were born around the turn the 20th century (Arnold Rothstein b. 1882 to Mickey Cohen b. 1913).

Source:

But He Was Good To His Mother Robert Rockaway - Gefen Publishing House - 2000