New Jersey is positioned in the NYC metro area and the Philly metro area and is largely a suburb of the two. If the Mafia has a presence in NY and Philly, they're going to have a presence in NJ, where a lot of mob guys live. Also Italians are the largest ethnic group in the state. It also has the nations 8th largest GDP.
That goes a long way to explaining it, especially the large Italian presence.
