Because the game has lost it's identity and given into the easy way for every body. I dont enjoy doing the same raid on multiple difficulties because when i kill a boss i like to move onto the next boss and look forward to learning the new mechanics and seeing a new part of the raid. That is now over with multiple difficulties and really gets boring so fast.
HC's are far to easy and have very little challenge to them, I started playing in TBC and loved the way u had to work together to get through it and had to really concentrate to complete it. Now it's just all about doing it as quick as possible with as little effort possible, I am like a robot when i done hc's after TBC. i'm just on auto pilot not really thinking of what i'm doing because it became way to easy.
Everything is the same and gear is to easy to obtain. Every class looks the exact same because there is different versions of the same tier and the game is dumbed down so every body can get gear with minimal effort. I believe Blizzard should make 1 very difficult raid and 1 raid for the casual/bad players that look completely different have completely different bosses to not make the game so predictable and similar.
I used to love the way u worked ur way up through the tiers and went at my own pace to reach the next raid. Now every body is on the same content when slower guilds do not have to take there time any more and instantly move onto the next raid even if they have not completed yet because the new HC's provide the same gear as the current raids.
The game used to feel like it was an epic adventure that would never end because u had so much to do, now everything is the same most people lack commitment and dont care any more. Before groups would stick together to finish the dungeon/raid now people leave instantly after 1 wipe and try again with a new group because they are not bothered to put the time in.
I used to play any where from 5-10 hours a day without getting bored in WOTLK i felt the game had went backwards after 2 weeks i was wishing We still had TBC. The 1st tier of Cata was very good imo my only criticism was the normal/hc of the same instanced/raids other than that it was perfect. I quit just before Firelands came out because i knew 6 bosses would not be enough to keep me interested in the game and ofc doing them on multiple difficulties just makes it even more boring. The game tried to keep catering to the player who didn't have much time to play or was not very good and in the end it ruined the game i loved.