To be utterly frank and honest; this should have been seen coming a mile off. Or, rather, right around the time Halo3 ODST came out. Bungie stated after releasing Halo 3 they were done with the Haloverse. They were ready to move on to new projects, so much so they sold the Halo IP to Microsoft to get their creative freedom back.
After Halo 3, I consider the series to be dead. Sure Bungie made ODST and Reach, but both titles are lacking in so many ways ODST more so than Reach. These are games that didn't really need to be made. The Halo story had ended. Earth was saved, the Covenant defeated. Unfortunately ODST and Reach were made to capitilize on the cash cow that is Halo with very telling results. Two games that are so lackluster one has to shake their head and think, Bungie made this?! This is pretty much what happens when publishers force developers into making games they would rather not.
Quite honestly we really could have done without ODST or Reach. What should have occured is Bungie was allowed to move onto the project they wished to do and more than likely we'd all be playing a new IP from Bungie right now, instead of playing a half hearted pile of repetative mediocrity with flashy graphics.