One major difficulty I have with World of Warcraft is that the buttons I have for each character have changed so often over the life of this game. Which means that even on my main character which I have played literally for thousands of hours I can’t remember the optimum sequence of button presses after a year and a half of not playing the game. That doesn’t appear to matter for quests, I can do those with just randomly mashing buttons, but it is a serious barrier to re-entry if I wanted to play again.
The next thing that hit me was getting billions of artifact points thrown at me for doing not much. It basically made all the effort I had previously put into artifact weapons seem pointless. On the other hand, I had stopped playing with only part 1 of the achievement necessary for flying done, and it turns out that part 2 still needs weeks of grinding to get to. No thanks!
In summary, World of Warcraft has changed the details frequently (which makes it hard to remember how to play well), while not changing the basic structure of the game enough (which makes it hard to find a renewed interest in playing). I still don’t think I will buy the next expansion, Battle for Azeroth.