Legit reasons include LFR and PuGs becoming more difficult because it did require (extremely bare) minimal effort to at least make it to 90, and there is currently a glut of new players who have never read a guide in their life and are overwhelmed with new buttons.
QQ reasons are because this game is all about epeen for many people and the lack of leveling time invested is one more thing to rage against.
Personally I don't mind it being in. LFR was always a cesspool and people who know how to play or are serious enough to learn will quickly move on to flex and "real" raids, just like they did without a boost after facerolling their way to 90. The casual players and outright bad ones will languish in lfr. Nothing will really change in the long run.