Im guessing that a lot of people who loved Simcity pre-ordered this. On its IP strength alone (just like D3 & present company notwithsdanding). I would also hazzard a guess that a shitload of people/kids/young adults who dont have a clue what SimCity used to be, but played the SHIT out of the myrad of The Sims games also preordered this on the pure marketing hype and the very similar art direction this game took. (This is not an accident, these games look similar for a damn good reason)
I think they sold a shitload. They probably dont want to release numbers now because it would be embarrasing for them to admit that millions of people worlwide cant log in and even play the damn game.