Microsoft acquired Bungie and its "Halo" franchise in 2000, a move that secured the wildly popular gaming franchise specifically for Xbox. In the end, it sounds like the Bungie guys had wanderlust, even though Microsoft wanted them to stick around.
Said Bungie cofounder Jason Jones in a statement: "Bungie is like a shark. We have to keep moving to survive. We have to continually test ourselves, or we might as well be dolphins. Or manatees."