The Cherry Hill guys earned, and Bruno got a cut. Caponigro desired bigger drug profits, and thought with Bruno out of the way, and him boss, he can usher in an era of drug peddling, the same thing the NY families did. With Stanfa in place as one of the co-conspirators, and his own ties to Cherry Hill. Perhaps Cherry Hill felt they could earn more in Philly, if the whole family was involved, instead of just a boss taking a cut out of THEIR profits. Maybe that's why they did nothing about Bruno's murder other than send floral decorations.

I'm just guessing here, I don't know the actual reason for the Gambinos allowing Bruno's murder, but they did.