Was it really THEM who turned it in just another organized crime group? I think it was more the consequence of the natural death of extremely powerful and charismatic characters like Carlo Gambino, Tommy Lucchese, Philip Lombardo etc that did the work, rather than the law enforcement. I can't know for sure, of course, but I think that if those characters were still alive and in power through the 80s and 90s, then the mafia would be weakened only in the 2000s. Human society is too corrupt and hypocritical to allow somebody like Carlo Gambino to get a life sentence or 100 years. It was difficult enough to give life even to a stupid thug like Gotti.