It's not about racials; its about being able to be the "bad guy" which for whatever reason is way more appealing to the newer generation than just being the "average do-gooder". Take the movie "Joker" or "Suicide Squad" as an example, even though they are the bad guys they are idolized, and those movies do x100 better than Batman or Superman. Take the Warcraft movie as an example as well, they portray the Orcs as being misunderstood. There have been several articles about the population on Classic WoW (not Warmane) that Horde out numbers Alliance 4 to 1. Its a common theme that is playing out across all the realms and servers I play on, both private and retail. It's weird but that's the core of it IMO. The Alliance at face-value is prim and proper which just isn't popular in todays world. I'd say the majority of the Alliance players are older or fans of other media (like LotR or GoT). Then theirs also the argument of "Its fantasy why would you play something dule like a human when you can literally be a minotaur?". Look at the advertisments for the new D&D Beyond, im not even sure what it is but they don't even showcase playable human characters, all the focus in the add is on playing as Orcs, Tieflings, Minotaurs, ect. Its also apart of "wokeism" and considering everything from other peoples point of view. In my day we just accepted the Troll was a bad guy, in todays world they try to rationalize what went wrong in the trolls life and sympathize with him.
Edit: I just wanted to add, the Horde has found a fix to their chronic losing, the last few days I've seen 3-4 teams with 6+ Hunters. Silencing Shot is completely shutting down all other RDPS and Healers.