Originally Posted by
Ielenia
I'm fairly sure Kil'Jaeden is the last villain of TBC, not Illidan.
And while the trailers are indeed supposed to give you a "hint of things to come", those "things to come" are stuff that happen in the beginning and maybe in the middle of the expansion, not in the finale. That'd be like the Avengers: Infinity War trailer showcasing all the heroes including SpiderMan being dusted.
For TBC and Wrath, Illidan and Arthas were the villains that set things in motion. You knew, from the get-go, that what was going on was set off by those characters.
Also, funny you didn't mention WoD in your little list, which had the Iron Horde, yet the expansion's finale was about the Burning Legion...