I suppose they could have been sent to help with the Feralas problem I mentioned, since they sure aren’t in any BfA areas from what I remember. They could be there at first with the Stonemaul Ogres, with the Dunemaul popping up shortly thereafter when the player character arrives. I’ll have to think on the Draenor Ogres some more.
Now to explain the Alliance attack a bit more. The Alliance’s interest in Dire Maul can come from the Void Elves, High Elves, and Night Elves in the Alliance, wanting to reclaim it, learn magical properties from it, and turning it into an Alliance outpost and such, so the Alliance would be keeping an eye on the Gordunni army being gathered by Mon’Morokk.
As they’re spying on the battle and see the Horde win and how the Gordunni are now joining the Horde, a message is quickly sent and the Alliance is panicking. The Gordunni have a lot of territory in Feralas, are destroying the area, have done some really not-nice things in general to the Alliance, and the Horde would be getting a huge advantage in the area. A decision is made to attack to stop the Gordunni from joining the Horde, possibly defeat the Horde there, and then take over Dire Maul afterwards. Thus the attack.
Of course, as mentioned, I see either the Horde fending them off or a stalemate occurring to promote a possible warfront in Feralas. The latter could be more interesting.
I’m having a lot of fun fleshing this out!