Well, the devices, future and present, want to do a lot of things that traditional typesetting can’t do. Having known page and type sizes is an assumption of print, but goes out the window when one wants to put a piece of content on different devices.

But I absolutely agree that the book is a valuable, time-tested format. We’ve learned a lot about readability. Conflating the goals of books and web pages would be a loss. NB, we still have radio.