Because video games are a medium that can tell stories in ways book and TV shows can't. I'd like to see one of the oldest players in the biz to show off what story-telling in video games can do,
One that never gave much of a shit about narrative, mind you.
If you *want* games to have a good story, look at games build from the ground up around narrative, David Cage's stuff, Alan Wake, whatever, don't interject narratives in existing series that never had (and don't need) a good story. Any miniscule dramatic tension in a Mario story would be cancelled by the innherent ridicule of the premise.
Even some of the older games had story. Granted you had to read the manual to find out most of the story, but it was still there.
Only as a throwaway justification for what you're doing. Frickin' Arkanoid has a story, should the next inevitable rehash show off what vidya gaems can do as a narrative medium?
There actually was a Tetris title (yes, Tetris) that added a story to explain why you're pilling up colorful shapes and why you should care. And guess what?
No one gave a shit. That's because Tetris is strong enough that it doesn't need narrative to justificate itself, and indeed, it's so entrenched in gaming conventions that trying to make a story is ridiculous. This is the same thing with Mario.