After an expansion of accessible raid content, unique and painstaking environments, and a storyline built up for more than five years: it followed with a difficulty shock, unpolished and unfinished environments, and an uninspiring plot. MMOs weren't the next best thing anymore, and a lot of people took it as their cue to move on.

I didn't find the right solution from the Internet.

References:
http://www.mmo-champion.com/threads/1359667-What-went-wrong-in-Cata

Motion Graphics Video Example