They were going the wrong way with TBC imo, massive amounts of casual features implemented especially the gear was much easier to obtain which kills uniqueness and longevity , and the worst gimmick of all flying mounts. Raising the level cap was also a huge mistake. The thing the nailed in TBC is the combat. As soon as Activision merge happened TBC was announced the game got alot easier and everything started to become monetized, and of course that continued. Vanilla at the time had at least another 2 years of life content wise, but of course at the time Activision wanted to capitalize on a game that was growing rapidly and created system just like their CoD series where they release a game every two years, the trick is to raise level cap so you have start again each expansion.