Bungie have been working on halo for around 10 years now, so they finally said goodbye to Halo. It's not that they're fed up of working with Halo, it's just they want to work on a new project. Microsoft will continue to make the new Halo trilogy so fans will not be dissappointed.
Here's an hour long documentary of how Bungie started and where they are now. If you're a halo fan I truly suggest you watch it. It made me feel like a proud, emotional parent.
Sorry for the short post guys.