Don't over-analyse it too much, some game-mechanics just have to be that way for game-mechanics reasons even if they unfortunately make no sense in the lore.
One big example: Players need respawning, so in the lore, Kami and Karavan can resurrect homins. And Marauders hate both Kami and Karavan, so no respawning for them. And seriously, how suicidal is it for a group of homins that stays dead (Marauders) to attack a group of homins that's effectively immortal (us)? Makes no sense no matter how you look at it.
Anyways, just wanted to add, don't forget the Marauders are made up of multiple mostly-independant tribes as well. So there's lots of room there for politics, differences between tribes, infighting, etc.
One big example: Players need respawning, so in the lore, Kami and Karavan can resurrect homins. And Marauders hate both Kami and Karavan, so no respawning for them. And seriously, how suicidal is it for a group of homins that stays dead (Marauders) to attack a group of homins that's effectively immortal (us)? Makes no sense no matter how you look at it.
Anyways, just wanted to add, don't forget the Marauders are made up of multiple mostly-independant tribes as well. So there's lots of room there for politics, differences between tribes, infighting, etc.