See, funny enough I burned out towards the end of Burning Crusade (before the Kil'jaeden thingy) because my wife and I were playing everyday. Tuesday and Wednesday was the Vashj raid, Thursday Friday and Saturday was the Kael'Thas raid, Sunday and Monday was either working towards Illidan or killing the Giant Ogre and/or Pitlord guy. On top of doing dailies.Except here it took people 5+ years to get tired of it and it wasn't the help that brought wow down, it was the crappy dungeons and raids of Cats and Mist. Wow at its heights in Wrath helped you along while still telling an amazing story, having fantastic dungeons and raid content.
My wife didn't have a job at the time and spent all day farming for potions for herself, myself, and the guild main tank. We had responsibilities that constantly kept us engaged, but not in a fun way anymore.
Funny enough, when I look back on WoW and think of the good times, it's almost never to do with Raiding. I remember getting my Tier 0 helm from Scholo after the 27th run. I remember my very first Epic I ever got [Headmaster's Charge]. I remember all the random ganking in Hillsbrad. I remember playing my first Alterac Valley Battleground for over 6 hours before I absolutely had to go to sleep.
I DO remember exploring Outland, but that's about where my good memories stop.