The difference is that a lot of roles in film are individual. You can hire a director, a writer, a scenarist, a bunch of actors etc. separately and they will do

The difference is that a lot of roles in film are individual. You can hire a director, a writer, a scenarist, a bunch of actors etc. separately and they will do their job just fine. And for the tasks, which require high-skill teamwork, movies contract a company, which employs the team full-time (e.g. VFX, stunts). There are very few individual roles in games. Even leadership roles are highly dependant on their teams (just look at what happened to Visceral if you want an example). And there is a lot of interdisciplinary interaction too, so even if there were separate game programming, game design and game art houses, there is no guarantee their could work with each other in a productive manner. At best you can separate QA and some art teams, which already happens all the time.