Reading is not an alternative to listening. Both have different use cases. You cannot read while driving, to name just one.

Using different voices to read different parts of a book turns an audiobook into a bad audio play, and arguably, a bad audio play is worse than a mediocre audio book.

What audible misses is, that, while reading is a technique that can be automated, narrating is an art. They can use AI to read books, they cannot use AI to narrate books.

Your example of AI use is a good example of this: AI can read your content. AI can enhance your capabilities. But only you can narrate it.

Did you ever heard a single AI-narrated content that did not make you run away screaming?