For the campaign im running I want to center it around a fortress world/system, example caida from 40k. Im having trouble justifying why enemy forces wouldnt just go around the planet and ignore it due to the way drift travel works. I want to avoid explaining it away with some sort of special magic plot device so im looking for some lore friendly suggestions.
For background the planet is in the vast, and is garrisoned by a combination of nyarthlotep cultists, Eoxian undead and hellknights along with a large militia comprised of peoples from various pact world colonies and protecterates from the surrounding systems.