That's an unfair comparison though, PD are doing what they love, cars and racing (even outside the gaming World).
Halo is just a game to Bungie not a lifestyle choice. I imagine they may feel creatively stunted by being "forced" to do Halo and are bored of it.
Halo was on napkins at Bungie long before MS bought them. Halo/Bungie is no different than PD/GT.