Some people believe the story was starting to get to close to the games, so Microsoft flexed their muscle. The actual people behind Halo: Faith aren't saying.
There is a petition online, haven't found the link yet, though. But, the Halo: Faith guys don't want to release this thing. Faith was just a big, expensive demo tape to them. I jokingly commented on their FB page, that when they make this "Feature film opportunity" that, when the credits begin to roll on said movie, the first thing they should say is "Dedicated to the fans and followers of Halo: Faith - You made us what we are."
For some reason, this is just really pissing me off today.