It's still a business though. And bungie needed to sell. Maybe they liked activision that much and only wanted to go with them. It's much like record producers. Bands come to a record producer to write music, but what that producer says goes. If you follow certain bands close enough, they will disclose sometimes that entire songs get chopped in pieces and put back together again, because it's what the producer thinks will sell. A huge reason why there are bands that have self labels now.