I'm going to very quickly sum up why MoP's PvE endgame is unable to keep casual players commited to the game:
- There is a lack of challenge
- There is no real sense of character progression
- There isn't a proper system in place that rewards attaining better results or putting in more effort
If Blizzard wishes to fix their problem of 'lack of commitment from casual players' then above are, in my opinion, the three main obstacles they need to overcome and find solutions for. Lack of commitment from a major part of the playerbase is perhaps one of the biggest flaws of Blizzard in the history of their game design, considering Blizzard games always used to be highly addictive and fun. But apparently Blizzard seems unable to find the right game design formula that would make casual endgame addictive... and fun.