You don't read, typically, for fact-ness. The more facts you know doesn't mean your mind works better or you're smarter. Those are pretty much separate things.

Books are mostly for comprehension and critical thinking.

The problem with facts is that they're a bit anti-critical thinking. They're just true - there's no debate, or philosophy, or introspection.

Fiction makes you think. About the world, about the future, about yourself, about who you want to be, about what life is about, about why you exist, about love, about injustice, etc. Facts don't really do that.