The question was how is the value of the labor of an author different from the value of the labor of a plumber. There is a difference, and part of the difference is that if someone wants another sink installed tomorrow, they have to hire the plumber again to do another days work, while the authors work can be copied for free and, if allowed, a company will happily pay the author $50 one time, and then resell that same work 500 million times over for $50 each.

The point was not to defend the current copyright system and certainly not some of the more notable abusers. You asked a question, and that that is one part of the answer. Writing a book or doing any form of creative information-product work is different from doing physical-product or service work.