Reason as to why none from Negans group kills him: He gives you a choice on what you want too do. If you're one of his henchmen; You live like a king. Why would they ruin that just for the sake of being in charge? Maybe they don't want to be in ; They're living good after all.
Then there's people who work for points. That is their choice. They could've been one of Negans men but instead they choose to stay behind at the sanctuary and work their asses off.
Then theres the prisoners like Daryl who have no input and have no choice but to do what they're told.
The system that Negan has doesn't require anyone to revolt, well, because they chose to be in their position. Maybe they don't like it (the pointers & prisoners) but what are you going to do when negan has men that will do anything he says because he gives them whatever they want for followng him & being "like" him. There's way more of them than the others.