I thought some sort of time related reason would really explain the unique planar aspects of Athas, regardless of the exact details each DM implemented in their personal campaign.
And with the outer planes being temporally empty, that could allow those faith conduits to be conscripted by the Elementals and the Dragons… but without proper linkages or access to the outer planes, it would be much more limited, ie: what we see on Athas for Clerics, Druids, and SKs.