Movie Studios do not respect Computer Games as a legitimate form of art, just a way of marketing a genre to an in built audience. It is the same situation with Comics and to a certain extent, Animation. Both of these artforms are considered to be just for kids and even now, are still not taken seriously by the vast majority of people.
Computer Games differ from Animation and Comics in that both the aforementioned mediums have been around long enough for talented film makers to take them seriously. I believe this will also happen with Film properties based on Computer Games.