There are at least as many reasons why people quit as there are people who quit. Basically what the haters can never accept is that different people like different things and that their pet issues are not the issues of others.
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Are you seriously saying everyone quit for the same reasons? You do realize during Cata there were simultaneous threads claiming the game was both too hard and too easy right? You have to realize Blizzard is catering to a diverse audience and not everyone is going to be happy with everything nor does it mean any aspect of the game is objectively bad. Again different people like different things but again like I said people like you tend to be butthurt if anyone dares not share your opinion of the game.