They are all mobsters/LCN but it is not like they are fighting over traditional rackets. It's primarily over distribution channels for cocaine and heroin. While always being an underlying income source for LCN, its not the traditional stuff a boss of a Five Families family gets knocked off for. The Rizzuto's goldmine was drug distribution through Canadian ports operating through the Cuntera-Caruana clan. It wasn't someone trying to eliminate Rizzuto to take over as head of MTL, it was someone trying to eliminate them completely to take over the drug importation.