Recently the alpha predator figure was released by NECA and because it appears in predator hunting grounds it means it and its backstory are canon. I’m not going to go into the whole thing but basically the predators were modified through gene manipulation and sexual selection into the modern predators by a slaver race called the amengi. A predator named Kaail who was a gladiator slave in an arena organized a rebellion and once free he and the other rebels became the first predators.
This tells us the predators, or at least Kaail’s breed of predator were bred to fight, but not for war. They were made to put on a show. The honor code might have been built into them to make for an exciting fight, motivating them to fight dangerous creatures and not to immediately annihilate weak opponents. The predator’s caste system is based around taking down lots of dangerous prey, similar to how gladiators earn fame by taking down dangerous opponents and getting many kills. Taking trophies of the hunts would serve for them to be shown off to the crowds later.
This explains why bad bloods are so hated. They aren’t just breaking an honor code, they are psychopaths that go against their own biology because they don’t have the honor code built into them, similar to how a serial killer doesn’t have empathy.
This is further reinforced in Alien Vs. Predator: Requiem. In it a predator is impregnates by a predalien and goes loose. Aliens take some genes from their hosts to adapt to the host’s environment and to not be detected by antibodies. Interestingly it possesses unique behavior that resembles a predator’s. First is the fact it’s seen taking a man’s skull and spine. This doesn’t make sense because Xenomoprhs are animals, but if taking trophies was a biological impulse it’d make sense. The predalien doesn’t understand why it did it, it just felt like it. Later on when facing down the predator Wolf, it waits for him to remove his mask. A xenomorph wouldn’t have given him the time to do that and would have attacked immediately, but it had an impulse to give him a fair fight. A predator removing his mask is a sign he and an opponent are going to fight “mano a mano”.
In avp:r the predalien tries to start its own hive but in the video game avp 3 the predalien works on its own away from the rest of the xenomorphs. This might have been a case where the predators biological impulse to hunt outweighed the xenomorph’s need to work with the hive.