Well, the easy answer is they wouldn't.
I love video games, and love some of the touching stories they tell. But video games are lacking a very important thing that books, television, movies, and other artistic media have: the oneness of the storyteller.
In a movie or book or TV show, the creator displays his creative vision to his audience. The audience members receive the vision and can interpret it in any way they choose, but they cannot involve themselves in the storytelling process. In video games, however, the audience is part of the process. So the artistic vision of the storyteller in video games is modified by the player, by the simple act of interacting with it.
Simply put, video games are interactive art. And that's why top storytellers might pass up video games in favor of other media that allow them to tell their stories.