Funnily enough it's probably because contrary to popular belief Microsoft are a excellent business partner for third parties and offer the best chance for the project to be marketed properly as a blockbuster new IP. They may as well take the aid from Microsoft to establish the IP with less risk then port later down the line rather than gamble the company on the success of one project.
LOL at the timed exclusives comments, get used to them, you'll be saying it a lot this gen.







