Answer here is probably a game design timimg. (when building prophecies, the designers just used regular terrain for all the areas, so crystal desert was a regular desert. Wehn making Elona, they needed something cool to make it stand out, so added the sulfur) However, it is interesting that the whole area was supposedly created at the same time, but the area south of mouth of torment somehow became sulfurous and craggy, but the northern area is flat.
Any thoughts on this? (I'll be back later with my own as well).