It was only going to be one of the Big 3 (Activision, EA or Ubisoft) to sign on with a major developer like Bungie. They weren't going to do this with just any publisher. JUst happens that Activision were the ones who jumped first. This agreement came to be all the way back in 2010, back before we knew anything any of games out now, so it was strictly a decision Activision made to get themselves a fresh franchise aside from COD, not relying on it.