And yet worlds that you can't explain abound. Worlds with diameters too small to retain their atmospheres. Populated airless worlds with technologies too low to support life. Worlds with populations too low to sustain their tech level. Garden worlds on the edge of Hierate space with no Aslan settlers. Trade hubs with no trade. Boatyards on worlds with no customers. Shipyards on worlds with no aupporting infrastructure. Transient populations accepted by the Imperium as legitimate. Low-population worlds that are being left alone by greedy neighbors. Independent worlds with populations too low too sustain themselves. Worlds with absolutely no correlation between habitability and population.See, the difference, though, is that I embrace those peculiarities and don't find them unbelievable or unexplainable.
Granted, some of these worlds can be explained away by invoking the Ancients or once-in-the-lifetime-of-the-universe happenstance. And I'm perfectly OK with that. Every once in a while. But not over and over again. If the rare and unusual becomes commonplace, it ceases to be rare and unusual.
And then, of course, there's the opposite side of the coin, the stifling of any ideas you may get unless they just happen to fit in with the UWPs. You might get a splendid idea for the history of a world and its neighboring colony, only in order to work properly the colony world has to have half a million inhabitants and the UWP says pop level 3.
Hans