That's because the gap between comic books and animation is one of the smallest between mediums. Not that it doesn't take creativity to adapt a manga into anime

That's because the gap between comic books and animation is one of the smallest between mediums. Not that it doesn't take creativity to adapt a manga into anime, but there is a template for a very faithful adaptation that is available to you. If you're turning a prose novel into a tv show, you have to basically create everything from scratch. You can set it in the world of the novel and basically follow the plot, but the pacing is impossible to translate directly, and you don't have any of the visuals.