We’ve seen many of the largest social games experience traffic losses in recent months, even as many smaller ones have grown. Over the course of September, 15 of the largest titles have shed monthly active users. That said, only five experienced significant drops of over a million users, and they tended to be older.
Likely, the losses are of no significant concern, but are merely a product of natural decline. Simply put, the longer the game is out there, the more people will become bored of it.