Originally Posted by
Hitei
First, the Horde does not have the resources or troops to "fully" control Kalimdor. They burned down Teldrassil, that doesn't mean they have the forces to control the entire northern side of the continent. Hyjal, Winterspring, and Moon Glade are all locations the Horde would have difficult assaulting. Not to mention that after Teldrassil, I can't imagine the Cenarion Circle is particularly happy with them, and assaulting Hyjal or Moon Glade would mean a direct confrontation with the Circle, the Ancients, and the Green Dragonflight.
Not exactly the best choice when they are already engaged with a very dangerous opponent.
Second, you mistakenly assume that the Nightborne joining the Horde means that the entirety of Suramar is joining. That is incredibly unlikely. It will almost certainly be a small splinter group under Silgryn who joins, nowhere near enough to take control of a mountain that, again, is defended by the Night Elves, Cenarion Circle, Green flight and Ancients.