>>43290728Amalathian.
As others have said, it's all about balance. While all threats to the Imperium are equally important, they are all equally important, and therefore it does not benefit anybody to have one group of Inquisitors, or any other political group for that matter save the Emperor Himself, holding too much power. Such practices are what led to the worst tragedies in Imperial history, like the Heresy, the Age of Apostasy, Nova Interregnum, and Goge Vandire.
They're also much more about getting the job done than they are about dogma. While they're still pretty hidebound by our standards, they're not above working with things like Xenos technology if it'll lead to a greater success down the road, the primary exception being anything related to Chaos. They aren't afraid to order the deaths of millions of people, but it also isn't their go-to decision.
They're basically rational people in an irrational universe.