It's a production with actors. Sometimes expensive ones. It's surely along the same continuum that explains why a 90 minute movie or season box set is more expensive than the book it's based on that takes weeks to consume. Wouldn't surprise me that consumers value it higher than "just a book."

Another way to look at it: that's 21 hours of content for $35. Doesn't seem crazy compared to, say, going to the movies or buying a $60 video game that might not even have 10 hours of gameplay.