Men are nasty and beastial. Mortality is high. The average age at death is young adulthood. Homicide is routine.
Tribesmen's lives are generally short. Brigands' lives are much shorter.
Traders, with their concealment and circumvention of conflict, stand a chance of longer survival. Guardians only expect to live until that day of dreadful hap: the day of tribal discovery -- the day of the guardians' doom.