If both sides are obeying a warrior code that lets you gain prestige but limits lethality, then you don’t want to defect by escalating the lethality of attacks, because then your enemies might too. Warrior codes are often part of a prisoners dilemma.
This is a late reply, but in some societies, intentionally not killing your enemy is the point. See counting coup in the Americas. https://en.m.wikipedia.org/wiki/Counting_coup
If both sides are obeying a warrior code that lets you gain prestige but limits lethality, then you don’t want to defect by escalating the lethality of attacks, because then your enemies might too. Warrior codes are often part of a prisoners dilemma.