There are few individuals as highly dedicated to protecting the land than the Elemental Priests.
Behind the Scenes
Back at the beginning of Dark Sun the designers wrote down a sentence that completely seperated the game from Dungeons and Dragons core, no deities. The thought was to make it a more difficult and deadly game, some players had several back-up characters just in case. However, the idea that there was no healing magic because deities didn't exist meant that the designers had to figure out a way to get around that idea.
The answer was the Elemental Priests, clerics but instead of praying to gods to heal they were essentially witch doctors. This was a great solution, players got their healing and Athas stayed deity free. But it was only a superficial fix, essentially they took the Cleric class and gave it a new name.
With the seperation of roles that came along in 4th edition the elemental priest was not as necessary. Instead of a Cleric groups could use Warlords, Druids, Shamans, or Ardents. For Dark Sun making healing more common outside of religion makes a lot more sense. The Elemental Priest was kept on as a theme for the edition and acted as a primal leader theme for those who liked the idea back in 2nd.