For one, the government has a huge hard-on for the Italian-American mafia. The least of noise any wiseguy makes and LE is on top of it in no time.

On the other hand, the government doesn't give a flying crap about African American, Puerto Rican or Dominican gangbangers stuck in their ghettos. Nor do they give a shit about a bunch of white trash living in NJ trailer parks. Sure they sell drugs (and a lot of it too) and shake down a few small businesses, but that's basically all they ever do. As far as LE is concerned, these gangs are fighting over chump change so they just let them have at it. Just let them sell their cocaine, crank, scag or meth so they can buy their Gucci or Moncler, their gold jewelry or so they can pay for the maintenance of their second Harley or Bentley.
From the moment the activities of street gangs will start to threaten things like legalized gambling, personal loans (like the banks do these days), big time economies (like unions)...then you will see LE start changing their tune about them.

The Mafia is seen as a threat; street/biker/prison gangs are seen as a nuisance. That's the difference.

And if we're talking about the lack of violence conducted by LCN...what about other organized crime "threats" in the area? Where are the "Russians"? Albanians? Israelis? Even the Chinese? Sure they're around, but they're definitely not dropping bodies left and right either.