If you're wondering why there may be hostilities between Microsoft and Bungie, then clearly you know nothing of the history between the two. There was a lot of tension between the two companies over the course of the production of the Halo franchise. You could easily find a couple videos on youtube that explain the struggle over development of Halo 2. I'm sure it only got worse as the original trilogy concluded and Microsoft wanted to make more. So when Bungie found a way out by splitting the company and giving up their franchise, they were probably in dire need of funding to make a new game, and probably the last thing they wanted to do is come crawling back to Microsoft. Also, I think it's likely Microsoft wouldn't want to support their next project anyways since Bungie found a way out of their corporate noose. So Playstation says hey we'll give a substantial amount of money to fund development as long as we get exclusives. And here we are now.