I believe it is to re-inforce the idea of the book as the product. A book page flipper is not meant for you to consume the content (must be annoying reading and

I believe it is to re-inforce the idea of the book as the product. A book page flipper is not meant for you to consume the content (must be annoying reading and having to see the animation on each page flip!), but for you to consult the material all the time being reminded of the physical object.