A rather large percentage of the top PvPers play human, especially in European servers, otherwise I agree. When a large percentage of world first quality Alliance guilds went Horde over the course of Cataclysm it very much created a trickled down effect where a good deal of 1st tier quality players switched, which lead to 2nd tier doing so in order to keep up, and on and on.
I know with WoD they say they are evening out the racials, which is a good thing, but the damage is done. If things are about equal in WoD, why transfer back to Alliance for no power gain? Just because you like the esthetic better? Those types of players don't generally care for faction pride, they go where they'll have the best shot of advancing.
Pretty much the only way to make a change would have been to make the Alliance racials overwhelmingly better to lore top shelf players to switch and then nerf the racials down to equality to the horde ones, a bait and switch.