I would argue that the medium of video games is more free to explore a rich story than either books or movies, video games benefit from the ability to explore story and lore asynchronously from the main plot, with unique branching, and at the players leisure, so appealing to a wide audience with every detail isn't necessary.

Some games can even continue story telling for hundreds of hours, meandering through dozens of different storylines, arcs, characters, minute details, (Skyrim, Fallout,..). Some games even have their own books inside the games that the character player can read!

The medium really is quite a bit more flexible than a movie. Where I think some comments are suggesting that games are not story rich enough to translate into movies and that's certainly true in some cases, I would argue that the types of story telling are simply not always directly compatible with a linear movie story line.