The advantage Horde holds over Alliance is not something you can easily see in game. Racials in the game today are largely balanced some might argue they are in fact tilted in Alliance’s favor with shadowmeld being unmatched in m+.

Years ago things like racials, faction-centric story-lines, and other faction specific differences may been relevant variables in the disparity of players on Horde vs Alliance.

The suggestions posed as solutions for this issue are often as incorrect and misguided as the explanations for why the factions are as imbalanced as they are in the first place.