I respected your opinion, until you mentioned Sims; possibly the most mundane and stupid game ever devised.
I could probably list a few reasons:
1. It's a Fantasy game, One of the only good Fantasy MMORPGs out there. For people like me who like stuff like Harpies, Pirates, Swashbucklers, goblins, orcs, elves and such its a real good time.
2. It's one of the largest MMORPGs - the game itself is almost 30GB in size at the moment on my drive, that's 30GB worth of explorable area and stuff to do in the game. If you know HOW to play; there literally isn't ever a 'dull moment' so to speak. There are hundreds of areas containing hundreds of quests for the level of player the area is aimed at. There are also 6 million players worldwide, it's rare that there's no one else to play with.
3. It's not that expensive compared to some other subscription games.
4. It's more 'immersive' than 'addictive', An addiction is something you can't stop doing regardless of how hard you try, Warcraft is something you never want to stop playing because it's a generally fun way to spend time if you're into that sort of thing.
People can get 'addicted' to any game if you want to use such a harsh word to describe it, i mean; how else does anyone get to 16th Prestige on Black Ops within a few months of it being released without playing most of the day every day? Maybe some people just like playing games; considering the state of the world at the moment, it's hardly surprising that people seek solace and acceptance within a community of like minded players. There are at least 3 or 4 other WoW players who are also active members here; i don't think i'll be short a little backup for my points.
Edit: I also notice it seems like you've never actually sat down and played WoW, It really bugs me how people can knock it without trying it.