I get where you are coming from and I think it comes down to your own personal experience with WoW.
In my case there were usually 5-10 people sitting on Vent chatting while playing. So it becomes a social outlet. Although I cannot find a link to it, there is a massive social aspect to WoW, that is underpinned by the concept of the guild.
I had some great times, but a lot of it was down to the people you played with on a nightly basis.
There was a secondary reason for me quitting, I was taking off three months to work on a couple of projects and the last thing I needed was some sort of game sitting there that I could play whenever.
Personally I recognise in myself that I have an addictive personality, but usually I pick up a game play it for a week or two then move on. With WoW it was the first game where the 'social' aspect became more important than the actual game. I was using it as a chat client. (Hint Blizzard bring out a RealId chat client!)
I have made many real life friends out of the game. I can only thank Blizzard for that, but I also recognise that the game has certain aspects to it that are not compatible with my life at the moment and I really wanted to make a clean break. Cata seemed the right point.