Why bother inhaling and exhaling? Answer: because we need to do it to live. Why bother writing books? Answer (at least for some people): because they need to do it to live. Not only is a book an author's contribution to society, payment for that book is a contribution from a reader to the author. It helps the author to pay the bills, and in most cases authors are lucky to get that much money. If an author doesn't feel the need for reader contributions, they are always free to release their book under a creative commons license or in the public domain. In that case, you can stuff the book onto your magical "knowledge server". Otherwise, it can't go on that server because it does not reflect the author's interests as governed by copyright laws.