I never went more than a couple of instance runs without getting something new, whether that be a drop, a reputation reward from bumping up to the next level, etc. And in between instance runs, I was generally crafting something, playing the AH, etc. The grind really wasn't that bad, and it's not why I quit.

Rather, I quit because I hit the end of the "non-social" content. I was at the point where, to progress further, I'd have to give up my random "whenever I feel like it" instancing, and cultivate guild relationships. I'd have to show up on time, stay late to help out, not bail in the middle of a run unless it was an emergency, etc.

Don't get me wrong, I've done all that before, and it was fun at the time, but I'm just not willing to put that kind of effort into the game right now. I'm willing to give WoW a lot of free time, simply because it's not very valuable to me, and I wouldn't otherwise be doing something important. I'm not willing to prioritize it over. . .well, anything, though, so I had to call it quits. Raids require schedules, and making one every once in a great while is not worth the monthly fee.