I don't think there's a problem with fictional works' authors being unknown or anonymous. The problem lies in nonfiction works that seek to directly convey any kind of knowledge or wisdom that is difficult to judge and evaluate independently on its own merits (with would cover just about everything outside the hard sciences). There is value in knowing the identity and character of an author, as well as the fact that they associated their personal reputation with the book they wrote.

For example, If I look for a book on developing physical fitness, I want to know who the author is and how fit or disciplined they are. If I read a book about history, I want to know how much the author has studied their topic, whether through formal scholarship or not. If I read a biography, I'd like to know if it's written by someone who personally knew their subject, how close or far removed the author was in time and space, and the kind of scholarship that the author is known for.

Identity and reputation matter when evaluating sources of knowledge in topics that you don't have the time to learn and master yourself.