There's a lot more to take away from books than just reading ability and story. You have to imagine/visualise the world the author is painting so it's a creative effort. You're inside the characters, hearing their experiences, thoughts and motivations which teaches empathy. The latter especially is typically missing from other mediums or done in a much more shallow way through flashbacks or exposition and is usually the reason "the book was better than the movie".

All that does come across in audio books though, you just miss the actual reading and imagining the voices.

Many people listen to audiobooks in situations where they can't watch or play things, like driving or working out.