That's how the mob survived for so long, by using violence only as a last resort. That's why Luciano and them created the commission, to avoid all those killings and all the mayhem that goes with it. When you go to war, you attract the attention of the government and the media on you, and above all you can't earn !! They are still using violence when they have to, but the time when the bodies were dropping in the streets are over, because it brings useless heat, fear among the ranks, and jeopardizes business.