> Chivalry, for instance, had a not coincidental effect of ensuring that knights were very rarely killed in most battles.

Which is the goal of any 'rules of combat' - to formalize the process in a way which reduces the actual damage done (or at least, the damage done to those writing the rules).

It's no different to the way cats will hiss and growl and spit at each other but will usually try and avoid actually fighting. Both sides have too much to lose unless a fight is really necessary.