Because Cata by and large totally missed the mark after launch when it came to new content, and the world rehash was and is bad. PvP was broke as fuck and dominated by stupid PvE items like the legendary Staff/Daggers/Gurthalak/OP as fuck trinkets. Vashir as a zone sucked cocks, Uldum made people kill kittens from disappointment, Deepholm was lame, Highlands were disconnected.
On the other hand the good stuff was spoiled by all the QQ from baddies in no time.
Firelands was underwhelming.
Dragon Soul raid and its dungeons (especially compared to the Troll 5mans) was a total and utter fail and disappointment. Difficulty scaling in Dragon Soul sucked too...everything faceroll until Spine then it went into OMGWTF mode, and then the Tentacle whack a mole was again easier.
The story can be resumed as... Everyone escorting Thrall.
There were no feels, no emotion, no lore, no ambiance. After WotLK people expected those feels, and got none of them.
The Goblins are meh. The Worgen are a massive let down. Great concept, half assed shit development, where most of the Worgen lore is actually on the Forsaken side...(what dumb fuckery is that?), while the Worgen themselves...well they end up living in a tree.