They could blow 200-300 million on a lot of feasibility studies, it doesn't mean it make any sort of financial or business sense for them to do so.
Completely wrong. What's the point in having mindbendingly enormous piles off cash and not using it to make even more cash, and how do you make cash, you muscle other companies out of business until you have a monopoly. They're already done this in the software sector, or at least as much as governments seem willing to allow them, so the sensible business plan for them now is to diversify into other sectors, use their bottomless pockets to wipe out the competition there, and form monopolies in those sectors.
Microsoft are being lazy. Capitalism has the same ending as Highlander. "There can be only one.". Microsoft should be ensuring it's them.
What's the point of having vast resources of cash and then pissing it away on a market sector so far away from both your core strengths, brand recognition value, corporate setup, experience/skill base and reputation as to be unrecognisable? MS doesn't have dominance or monopoly in any case; just look at the heating-up rivalry with Google and Apple in markets far, far closer to their market area. Even entertainment hardware like the Xbox and Zune are being 'done' because they are valuable as software sellers or for softening up the marketplace (and both are also using 3rd parties like IBM & Toshiba to shoulder costs and provide expertise).
Moreso, Microsoft don't have the facilities, skills or staff for making a movie; so unless they want to open up a studio and distributor for a one-off property (because they don't have anything else anywhere near as movie-marketable as Halo), they'll need to go via an established major studio. Because what sort of movie crew, etc, would leave one of those for a short term contract at Microsoft studios? So then you have MS paying the studio to make the movie.... and a distributor to distribute. In the knowledge that the movie game is fickle, too; the Doom movie cost $70m (half the estimated Halo movie cost, and that's assuming there aren't delay and budget increases) and only made $56m.
And if there's one thing big corporations know, it's risk management. Maximising ROI and all that jazz. So there's no way in hell they'll self finance, because it's a huge risk (not to mention the aside of negative impact on the game brand if the movie is ****e - and arguably the value of Halo as a movie is PR rather than money, which is why you want professionals
to do it); just look at the conditions they attached in getting other studios to finance it.