1. Repetitive - they tried their best with the different wings, but honestly it's just always the same: go through map, beat floor boss, repeat.
2. Mandatory - the rewards are fundamental to character progression, so you have to do it all the time, on every character, every week, for a very long time.
3. Anima Powers - they SOUND fun at first, until you realize that a lot of the time you just end up either doing the exact same thing, or feeling bad because of bad rolls
4. Bosses - Torghast has incredibly boring and simplistic bosses, a lot of the time they die in literal seconds and you ignore most mechanics
All of that combines to make a chore rather than an activity. Instead of something you WANT to do because it's enjoyable, it becomes something you HAVE to do because it has uniquely attractive rewards.
...which, when you boil it down, is at the heart of a lot of WoW's problems.