There were hundreds of Minor worlds surrounding Trion and, for one reason or another, not all of them had been chosen by the Empire. Most likely it was an issue of manpower. Rowan did know the reason why the God King had refused the growth of more Dominators and restricted their numbers, but he knew there would be no way for the Empire to conquer more planets.
There was an intense ongoing war upon the surface of Trion, that alone must be holding more than twenty percent of the total forces of Dominators in the Empire, there was simply no way that the Empire could continue spreading into more planets.
Plus some planets were simply too hostile, or barren or were filled with resources that the Empire did not lack or have the use for, so many of such planets were left alone, also some of these planets were privately owned.
