The video games that do have a decent plot often have a plot that just can't be squeezed into a movie. I've seen some decent anime conversions of some video games, which were arguably interactive anime anyhow (i.e., Persona 4), but at roughly 8 hours (call it 24 20 minute episodes by the time you're done with commercials, opening, and closing) and still feeling a bit squeezed at times, that's not going to be a movie any time soon. From a more western perspective, good luck getting Planescape: Torment into a movie format.

I supposed if Hollywood had some confidence about making video game movies they might be very excited about getting a pre-made trilogy, but since their lack of confidence is well-founded in fact I don't see this happening any time soon.