Pirates Had Some Standard Values
Even though pirates were really cruel and they were living by stealing and terrorizing, they had a set of values that they obeyed. For example, some of their values were dividing food and chores equally and never fighting against each other while on the ship.
They knew it was not worth even fighting pirates from other ships and tried at all costs to avoid casualties. The merchant vessels pirates usually plundered had small crews and were not posing a huge threat.