E-Thugs: Because calling people out in real life can be dangerous.
Posted by: BravoZulu
Posted by: fallencrusade
Because the covenant knew where the rings were before the UNSC did.
I was under the impression that from Fall of reach, it was Cortana who found the ring. The Covenant were able to follow the path of the Autumn and get there first.
Alternatively, the game is good at ignoring the book, so who knows?
I'm going to assume that the Fall of Reach is canon, seeing as there's no game within the same time frame that follows Master Chief. If one reads the book, you'll remember that when the Pillar of Autumn jumped out of Slipspace, it was met by a huge covenant armada. Also, Cortana discovered the coordinates to the first Halo off of a star chart that was intercepted from a Covenant corvette, which means that they at least knew about the rings and had a rough estimate to their whereabouts before the UNSC even realized their existence.