When I think back on my raiding experience in Burning Crusade, I also think back to my raiding experience in vanilla. There was much I didn't finish in vanilla, or didn't even start, and BC gave me another shot at it. With ten levels and a few tiers of gear inflation, I could go back for another crack at it. Certainly it was not the original experience, an inevitable thing given that we were acting as 10 or so people taking the place of 40, with new class mechanics breaking all sorts of old rules. But it was something, to intentionally misquote an old towel advertisement, almost, but not quite, entirely like the raids.
Treadmills don't give much sense of progress. We gain more levels and gear, and so do our AI enemies. So where are we now? Nowhere new. But we can get a sense of progress when we walk backward off the treadmill, thereby gaining a greater sense of our gain in power as well as the way this metaphor has gone off track. In BC I was stronger than in vanilla and I knew this because in BC I could solo Garr and a few other bosses, where once I could not even glance the wrong way at a trash mob. And in Wrath of the Lich King I knew I was stronger because I could solo Karazhan and bring small groups to other places as well.
The sense of being incomplete was part of what drove me. I'd tried and failed and now I would try again. There were bosses I'd not killed, interesting drops I'd not gotten, quests left undone, AQ gates, anyone? One could say that this is evidence of an elitist, overly restrictive game design. I don't think so. I much preferred to have something left over.
At the least it was a radical change of scenery and way of playing. Having raid content when I'm supposed to do that raid content is nice, but it gets to be the same thing over again, the same cruel loot tables, the same distribution problems, the same shortage of the same class or role, the same thing just in a differently painted room. Old raids offer something different. It's not quite trivial, it's not quite new and not quite old, it's entirely useless and yet, through that uselessness, entirely liberated. When the loot becomes a toy rather than a deserved, demanded reward, people are nicer about it. It's simply a different experience, raiding old raids, than anything else in the game. Raid old raids is a form of content, accidentally created with the Burning Crusade expansion.
But Lich King killed that. The rolling nature meant that I'd done all of the raids, except some of Ulduar which I was sick of anyway and that one place they added near the end that no one did. There was no sense of incompleteness. I felt as if I was done. Bosses dead, badges farmed. There was nothing I'd want to go back for, except maybe Shadowmourne, but by the end I'd grown to hate Icecrown Citadel. Too many months in the same place, farming the same badges, off the same bosses, with the most miserable architecture imaginable. Blue and grey are sorrowful, while at least the red and oranges of vanilla and BC had some fire to them, some happiness or at least rage.
When I felt stalled before, I could go back and progress in the past, going backward for another path forward. Lich King used up all the forward. So when I stalled in Cataclysm, I had nowhere to go back to, nowhere else to go forward, and so I left.