There is more burnout more quickly because there is sooooo much more things to do now rather than logging in during raid night, then logging out. There is actually content so people tend to play the game for longer periods of net time, therefore they appear to be burning out faster. For example: In Warth i logged in to do ICC, then logged out. In MoP, i logged in to do a Raid, then i did flex, then a challenge raid, then raid finder then timeless isle on an alt.
With that said, At least this is not a Sunwell Plateau: Destroyer of Raids type of situation.