There's several reasons why LCN is no longer in control of the drug trade.

1. Heroin is no longer the drug of choice. Back in the 1960-70's, heroin was the drug of choice. The heroin supply came through Sicily via the Middle East. It was natural that the Italian OC groups were in control of the wholesale distribution. The past 35 years cocaine has been the drug of choice. Cocaine comes from South America, so the Colombians and Mexican cartels control the wholesale. The cocaine either goes direct from Colombia to Florida or across the US-Mexico border. Why would those groups need or want the Italians involved?

2. LCN was never much into dealing at the street level. Some associates would do it, and maybe a few lowly made men. It was looked down upon and dealing in the Italian neighborhoods would get you killed back then. A white guy can't go into the ghetto and deal. The street level dealing was always dominated by the black and Hispanic street gangs. On the streets, violence and numbers rule. The Mafia doesn't have the numbers and violence would attract too much attention.

3. The stiff drug sentences keeps most guys away. Gene Gotti got 50 years for moving a few million dollars of heroin. Tory LoCascio got 5 years for stealing hundreds of millions through the phone and porn scam.