They didn't mate. See, back in... I think it was 1999, Microsoft bought Bungie Studios. They gave them the funding and ability to create Halo. Microsoft owned Bungie. Now after 2007, Bungie was tired of being owned. They wanted to become Employee owned again. They wanted the freedom to do what they wanted instead of what Microsoft wanted... and not live under the fear of being destroyed (Microsoft shuts companies down and repurposes the employees too often... it was scary). So after Halo 3, Bungie and Microsoft signed a contract that gave Bungie its independence. In return, Bungie had to agree to make two more Halo games. So they did- ODST and Reach. However, when Halo: CE was published under Microsoft, since Microsoft owned Bungie that meant they owned Halo. Bungie never owned Halo- it was not theirs to give. So in order to split off, they had to leave Halo behind since it was Microsoft that owned the IP. But it's OK. Bungie is now working on Destiny, a brand new universe. They have a fraction of the limitations they had before, and they have a blank check as to how they want this game to play like. It is going to be amazing, and I think you'll be pleased with what they come up with too. :)