Because pressure at the top is exerted downward. As an 8/12 Alliance Mythic Guild, I can tell you that the raiding scene is so bad on ally that it’s made recruitment basically come down to poaching and waiting to vulture from dead guilds.
And if you don’t think this effects you because you don’t raid mythic, and you play alliance, then I’m sorry to say that it does.
As the mythic raid scene dries up, lower difficulties will get worse and worse as the better players see no room for advancement and either faction transfer or quit.
This effects all alliance players. It’s not even about racials, it’s all population.