When you search for WoW on youtube you can see that the community is very weak, where a medium size League of Legends youtuber racks up hundreds of thousands of views, a WoW youtuber usually gets like fourty thousand at max. Why is that?
Well, I think that the whole MMORPG genre is dying, WoW is still doing fine compared to other MMOs, but still you can see the difference. The problem is that until you get to play, or atleast, until you can compete, you have to spend lots of time grinding gear and such, whereas in League of Legends you do not have disadvantages against other players, really. The leveling is painfully boring usually, it feels like a chore, you do not play the "end-game". The purpose of leveling is clear, but it makes the game so uninteresting.
What do you think?!
Wow Google Trends chart (last 5 years)
It is essentially a 12-year-old game. Interest is going to eventually die off until the next big thing. World of Starcraft, perhaps?