The writers didn’t understand. They didn’t have a good vision of what they were doing.
The Alliance’s milieu is that they are established, they have places of importance that carry cultural meaning and significance. They serve as touchstones for the character of the cultures and their identities. Stormwind for Humans, stony but reaching upward, sprawling but diverse. Ironforge being solid, squat, powerful and fiery. And remember Teldrassil? Calm, cool colors, deep forests with great old trees, home to hidden things and ancient knowledges?
The Horde’s milieu is that they have lost everything. They are wanderers, misfits, flung into savagery and forced to fend for themselves in a place that is not their home. Even their allies are marginalized, hunted or pressed beyond resource such that their defining trait is loss.
The writers didn’t seem to understand that in destroying Teldrassil they were taking more than they could ever give back. They were wiping away some of the essential character of the Kaldorei in a way that could not be answered.
The horde has nothing of equivalent value that they can lose. They have already lost it. There is nothing the writers can now do to provide even the illusion of parity. It was an uninformed and poorly considered decision that has become cannon and swept the writers into a corner they cannot exit.
Well… I say that… if I were to workshop it without bias I might say that the thing that the Horde has that is on par with a cultural identity is freedom. What if one of the horde races were to quit them and go alliance? Or get captured in some way and forced to serve the alliance? Maybe the Blood Elves rejoin all those other high elves that seem to be everywhere doing alliance related things.
What a blow to the Horde. What a crushing sensation to simply lose a chunk of the union they had fought so hard to build.
But that too would be a terrible idea, an awful writing direction and ugly thing to do to players.
And one thing that I understand (but the devs don’t seem to) is that putting one bad idea on top of another bad idea doesn’t make either one any better.