I don't know a huge amount about the background to the wow lore, because there are other fictional universes that I find are far more indepth and are more too my liking. Pandaria is another story arc, that has clues and new information about existing lore aswell as expanding on some existing lore. You learn more about existing characters and races. Alot of the lore in Pandaland is interesting, new and quite exciting to a lot of people and they aren't just completely rehashing the same stuff they have used previously. There is so much to it that is new and interesting and without it would be a VERY dull and boring experience like many other story's out there, rather than its own thing.
Also, Lore - The backstory created around a fictional universe.
anyway, I'm tired and my point may not be clear.