There are lots of factors there. In our timeline, the Spires of Arak are gone completely, and all Arakkoa are overtaken by Sethe's curse. They seek to spread the curse anywhere they can, thus why they're in nearly every zone. However, factoring in the story from our timeline has little to no affect on the events of WoD, since it takes place so much further in the past, and much of the Arakkoa's history has changed drastically between WoD's timeline and BC's timeline.
In the alternate timeline, the only major settlements of Outcasts are in Talador (and even then, those are relatively close to Arak). Kilrogg's Lords of War preview (and some other sources, I believe) mention some attacks from the Arakkoa against the Bleeding Hollow in Tanaan, but it's unknown if it's Adherents or Outcasts, as either fits the description (though, in this timeline it fits the Adherents more).
Either way, the Arakkoa in Ashran are out of place because of the fact that there are so few colonies/encampments of Arakkoa outside of the Spires and Talador. It's quite a ways off from anyplace else the Arakkoa have settled. And they're clearly not part of the Order of the Awakened, since they attack us on sight (and they're cursed, so they are probably Sethekk). To me, it seems they simply wanted to fill in that space, and give the Arakkoa a tiny amount more lore, so they stuck them there. It would have been much better had there been a quest, book, or NPC that mentioned why they're there, instead of somewhere slightly closer to all the other Arakkoa (and Sethekk).