To a degree, the cost of reproduction is kept high artificially through laws that protect intellectual property. Some time ago, society as a whole recognized that, in some cases, economics of producing intellectual property was a negative incentive to authors from sharing their IP with others. As a result, they put in place mechanisms such as copyrights and patents to encourage the flow of ideas. By providing inventors and authors a degree of legal protection, society seeks to ensure that they can reap greater rewards by making their intellectual property publicly available rather than keeping it secret. For written works, the real cost of reproduction is still relatively high because they are sold as physical property.
Books have a per-unit cost of production.
They are the preferred form because the physical artifact of the book is so well-designed and convenient to use. For extended reading, there is still no substitute for a professionally bound, paper and ink book. Once consumers own electronic books and there are digital networks in place over which publishers and consumers can communicate, distributing a book to a consumer electronically does not incur any significant additional cost for either party. There are two noteworthy impacts from this change. First, anyone can produce and sell their own books, since there is no longer an economy of scale to overcome.