I love this example. I can understand why the audio version isn't included for free with the text version: the voice artist had to work 40~50 hours to create it

I love this example. I can understand why the audio version isn't included for free with the text version: the voice artist had to work 40~50 hours to create it, akin to the coloring artist in your example. But the reverse doesn't make sense. When I buy an audio book, I'm already paying both for the contents and for the execution: surely the contents were already paid for.