So it's been about 8 or 9 months in game since I adopted the strategy of burning down the wooden buildings in cleared njerpez camps. In total I've cleared either 41 or 42 camps total (including 1 from initial scenario and two east of southern reemi not included in this screenshot,) and I think that number was 6 or 7 before I started. So in ~9 months I got ~35 njerpez camps to spawn.
So, if you're not getting enough Njerpez action where you are, move to no mans land between Reemi and Kaumo, roam around until you see those purple spots, then clear it and burn down the wooden buildings (you can leave the kotas.)
Side note but clearing all these camps led to the first time I ever saw an ango in game, and also a throwing axe.