It was because of the pandas. That's a reason a ton of people missed out on one of the most feature and content rich expansion to date.
It's also why we got WoD. MoP was a painful example, I think, where Blizzard saw that actually making content didn't seem to even matter, so they seemingly did the bare minimum with WoD, and at first, were rewarded for it because it didn't have pandas in it.