Lore can always be created to explain anything, it's how WoW got to where its stories are today.
Thing is there's still a large amount of people that value "tradition" and that's why it's comparatively slower shake it up. You get there eventually though, such as us finally having Troll Paladins, Tauren Paladins/priests, seeing the Void as "can be used for good not just bad" , all the new races we have and the more race/class combos than before (ie no Human Rangers at the beginning--as silly as that was).
But there's still people who hold onto "tradition". I remember back when my best friend and I went to pick up our Cataclysm Collector's editions and there was a guy in the store talking about "it's so stupid how there's dwarf mages now."
Some people just want the game to never move from a certain point, despite that being the foundation of MMOs -> to advance/change/improve.