That's a broader theme. Watching TV is considered more childish than reading a book, even though TV content requires a lot more kinds of creative work in order to exist. The reason is that usually when the medium is richer, it demands less of its audience. Instead of imagining a scene, you're given its picture ready-made. Instead of actively following the lines of a story, you passively assimilate what appears before your eyes. It's less effort, and it's less active. It's common for people to watch TV in order to "turn off their brains" when exhausted. "Turning one's brain off" when reading a book is usually an accident, not an intentional thing, and happens a lot less.

Games demand more from their audience than TV, but you're still given a lot to consume passively, compared to a book: instead of imagining scenes, you're again given them as pictures. Games do compensate though with demanding that you make choices as you play a game, which may impact a story. Well... that's as long as the game is not an FPS, or a racing game, where choices don't matter for a story, as the story is either non-existent, or barely important; and what matters a lot more is your dexterity and reflex.