Athas breeds god-killers. I’ll explain:
‘Dragon Kings’’ explanation of how the Sorcerer Kings were capable of granting their templars’ spells [i.e. the living vortices] always intrigued me as a kid. The idea of entities, external to the reality of the prime material yet connected to the prime via the Inner Planes and anchored to the SKs…I found the implied metaphysics fascinating.
Knowing that this connection was beyond the understanding or knowledge of the SKs at the time - that they were unique and siphoning the essence of these extraplanar entities by simply being - was another indication of how different Dark Sun’s approach to sorcery was in relation to standard D&D. Magic, defiling magic at least, had a corrupting, parasitic, influence on everything it touched…or that touched it.
This led to a few ideas concerning gods on Athas and the nature of the crystal sphere. We know, from the ‘Prism Pentad’, that the guardian spirits in the Crimson Shrine underneath Tyr worshipped a god from the Green Age and that their faith in that power kept the candles burning in the shrine. Knowing that gods are an irrefutable fact beyond Athas it’s not unreasonable to posit that gods are aware of Athas and may have interacted with the world in the past…so the possibilities are: gods never interacted with or had an impact on Athas; apotheosis, of a kind, existed via ascended elemental priests; or true gods were present, and for some reason, left, faded and/or died.
We know that Athasians, in general, are tougher, more deadly than their counterparts on other prime worlds. We also know from a few Planescape products that denizens of the lower planes admire and respect Athas’ defilers in particular for their sheer destructive power…simply through the act of preparing to cast a spell a defiler can corrupt and/or kill every living thing around them.
So, the point of this little thought experiment, the reason Athas is ‘locked off’ from the other planes, it’s divine conduits severed, is because it is a world capable of creating god-killers. Simply put, the other planes are afraid of Athasians.
Arcane magic-users native to Athas draw on life energy for power; at low levels, basic plant life; as they advance they can draw from more complex organisms. The most powerful PC in one of my campaigns became a plane-walking Defiler/Psionicist…23rd level…before he met his end. Imagine the havoc a mature Athasian dragon could wreak on the Outer Planes, places and beings suffused with rarified forms of magical life energy. Could a dragon drain an aasimon…or a pit fiend to fuel a ritual? What’s the upper limit?