Because just by looking at the Hall of Fame, it doesn't seem like it. Not to mention pvp.
Faction imbalance is bad as it is and will only get worse to the point where everybody and their mother will be playing Horde. And that will be detrimental to the game. Because the game is centered around the divide between Horde and Alliance, and you may not like that or aren't interested in it, but that is the lore on which most stories are based on.
If they ever go cross faction that will mean Wow is going downhill for sure, to never return. If you give up your main premise for a game, it's time to pack it up.
Rift did that with cross faction and look where they are now. If you can't sustain the main theme of your franchise, you're headed for disaster.