Fun fact. Pirates also didn't needlessly kill and rape, instead they expected you to either surrender so they can get the treasure or be idiotic enough to be defeated in battle and survivors tortured.
Fun fact, this was true for bandits too, unless they were the roaming kind.
Simply not worth killing your revenue stream to get all they have at that one moment, unless you are forced to (since you are then unable to demand tribute from them in the future too. Not to mention the road will get labeled as dangerous and those that did frequent it and aren't dead yet, will stop).
...Then some bandits smarted up even more, and realized they could tax nearby settlements, call themselves lords, and defend their territory from other similarly smart bandits.