At the start of the expansion doing dailies was not optional if you wanted to progress your char and improve gear, there were gear slots where the only option was to either farm dailies or wait until the next raid opened. Being in a raiding guild I was under pressure to farm dailies and I felt really annoyed that I had to farm my ass off with mindless dailies just to be able to spend the Valor points i'd earned from raiding, and don't even get me started on playing an alt and being faced with the whole bullshit again.
True that it is the issue was partly addressed, a lot of people quit before that came in. I stopped playing MOP WoW not long after Heart of Fear opened and I'd put a bet that part of that was burnout from the ridiculous ammount of dailies that I was basically forced to do in order to be able to gear.
Why do people dislike dailies? Because its a chore, repeating the same set of quests every day to slowly grind up some reputation is not fun, especially not if you feel that you "have" to do it. Its not so bad if it is just a few but with MOP it was just ridiculous, you had multiple daily questing hubs and that list has only grown larger (though it's not a necessity so anymore).
Ultimately it isn't fun, it isn't a part of the game that I look forward to.