What's special about the book? It's the cost, proof of work if you will. If costs nothing to write or read an internet post, so bots, cheap workforce and gullible people can be employed. Only selected few buy books, because it costs money, so it's their vote that counts for the author, the publishers and for fellow readers.

I see it from the other end - what counts is not the cost of producing the book, but the opportunity cost of the reader sitting down with a particular book. A computer or phone allows you to context switch to a million different things, and even an e-reader allows you to easily switch between hundreds of books. But with a physical book, you commit yourself to carrying, holding and focusing on a particular work.

There's something deep about this commitment, and I think we would get almost the same result if we had digital devices that were made to hold exactly one book, and you had to take yours to the library/store to return the old one and download a new one - such that even if the cost of copying the bytes is zero, you pay the cost of physically carrying that one book that you took the time to pick out.

> Only selected few buy books, because it costs money

I doubt money is the limiting factor for book uptake in the West, particularly in towns with a library. You're instead selecting for curiosity, intelligence and attention span. (Say this as someone without enough of the last.)

Writing digitally is cheaper but that's exactly why distributing or getting reach is not cheap at all. You still need cost and proof of work in getting noticed by algorithms, as well as people who usually set trends. In fact, the lower cost of production means that more niche things get written than there would have been a market for.