I’m afraid the reason they aren’t in the game is those marks are predominantly as a result of successfully hunting a Xenomorph. And being a Predator main entry title, I’m guessing they will avoid alien related lore where possible.
Which will be difficult as Predator Lore and culture is heavily laced with the Xenomorph race, making up a large portion of it, especially most ritualistic hunts, ranks and other culture milestones such as the rite of passage. Infact nearly all Predator hierarchy stems from their ability to prove themselves against Xenomorphs.
For example blooded Predators, which are most Predators we have seen in the movie universe, are ones who have killed Xenos, and to obtain the rank of Elite like Wolf, typically have had to kill a Queen.
Drifting from the point 😂 that’s likely why they haven’t included the mark. Although they should as even as a Predator title, removing the Xenomorph factor guts the Predator lore and stop being the Predators we love.
