There was a time when there could be substantial benefits for an Italian-American guy to join one of the families. Especially considering upward mobility in mainstream society was more restricted for one reason or another. Obviously that's no longer the case. Now, a smart Italian-American guy is going to want to make it big in the legitimate world rather than enter a life of crime. Especially a life that has been in decline for decades. So it's not only a case of attrition of quantity but also of quality. Less capable, less intelligent guys wanting to be in the mob.

Personally, I think the disappearing Italian enclaves factor has been overblown. The one upside, for the mob, of Italians becoming more ingrained in general society is they weren't confined to their own neighborhoods and only the rackets within those boundaries. They were able to expand which, among other reasons, is why they were able to bridge the upper and underworlds.