I think you need to take in to consideration not just weather there's younger guys available to replace senior members, or if they have shooters/heavy guys available to do work but exactly what the family has left to offer a new recruit besides a button. A lot of the traditional pools of income the mob has "owned" and can offer to a new member have dried up or at the very least been drastically reduced. Labour racketeering through union infiltration and the like is nowhere like it used to be. Standover and extortion is getting harder given most would be victims no longer fear retribution and its very hard to shake down a branch of some multi national company. Government restrictions on industry's like garbage hauling and transportation have put a crimp in the earning potential there. Even online and state sanctioned gambling and payday loan houses have to have put a dent in the bookmaking and shy industry. Beside the fact that as well as the actual members getting older and dying off, so are their contacts in legitimate business.
Im not saying this doesn't go on, but it aint a patch on what it used to be. This leaves drugs. Your now walking in a world of bikers, street gangs and the like or if you do manage to climb the tree ,cartels or large syndicates well beyond the scope of neighbourhood thugs. A smart criminal going down this road has to ask himself if being associated with an LCN family with its heightened survallience and close scrutiny is the best way to go. The days of a father or capo passing an ongoing racket onto his son/nephew/new member are over.
I think the way of the future for the crime family's is diversifying, like they have been, into the more sophisticated crimes...credit fraud, online scams, stock manipulation etc. which will lead to a smaller membership requirement and also a need for a more selective quality of recruit. I think this will ultimately lead to the larger family's slowly amalgamating the smaller ones as they themselves begin a refinement process for quality over quantity as a matter of survival. The mob can no longer stand toe to toe with some of the other big players that are not only prepared to resort to violence, its usually their first response.
That being said...there's always gonna be some young Guido that's watched the godfather and goodfellas one time to many and buys right into the hype..what do I know.