Why Haven't They Made a HALO Movie Yet?

I stumbled across this live-action trailer for the upcoming HALO 3: ODST video game the other day. Check it out:



I really don't understand why they haven't made a HALO movie yet. If this was a trailer for a movie, people would line up to see it. The other HALO game trailers have looked pretty good too. Here's one of the CG animated HALO wars trailers:



So there's no question that the game can be made to look great on screen. Now all that's left to do is find a decent writer/director team to helm the project, give them a couple hundred million dollars, and make something impressive. What are you waiting for Hollywood?