User blog comment:Gourgeist/Attack on Titan Season 2/@comment-91.133.158.218-20140805113136/@comment-12642484-20140805115804

Because Attack on Titan is based on a monthly released manga of the same name. There is not enough source material for a season season yet and if they release the second season too soon, then you will have to wait 5 years or more for a third season.