They're in this position because the current stories are rally, really bad. There is no intrinsic problem with telling new stories; they just need to not be bloody stupid, donated by tropes, incredibly derivative, and so on.
MoP was a god damn fantastic expansion with a small amount of incredibly loud naysayers who thought pandas were stupid.the people actually there, playing it at the time, loved it.at least most of the ones I played with. The leveling experience was great, the story telling was largely great, the raids were a mixed bag but some were among the best ever released, the PvP was fucking awesome..
When you compare the experience playing Timeless Isle to say, Tanaan, or compare Isle of Thunder and Throne of Thunder to anything comparable since, they are just different experiences. MoP was loved. I didn't love everything about it but even the stuff I didn't love I could see that it was made by someone who wanted me to like it because they liked making it. It's very different to what has come since, where the majority of the content in a similar vein simply feels like a way to make me stay in the game, rather than a way to make me WANT to stay in the game. The broken isles and antorus just make me shudder, they were made by people trying to extract my time soullessly.