Because of the price, and NOT the content? Granted... 4.1 was a bit bare...
But I know plenty of people who had to quit, or even start because of the prices. If someone new wanted to play, they're looking at 100$ + the 15$ a month.. quite outrageous.
I think that they should make it where all you have to do is buy cataclysm.. But I'm not Blizzard, I'm not genius, and, it's their problem.