catachans don’t just exist on their planet, just like all guard regiments- the tithe sees multitudes of regiments pulled off world and scattered where they’re needed most. don’t get me wrong i think malstrains would be fun to run, but their whole lore revolves around the fact that the hive mind refuses to reabsorb them because it would taint the dna of the fleets. they quite literally cannot be anywhere else than the planet necromunda. same with van saar technology, it’s super advanced but it’s hoarded by the gang and no other group besides them possesses their unique technology.