It isn't really. Copyright laws took into account the difficulty of creating & distributing copies. In the past 30 years that has been condensed, what, 1 million times? One can very well make the case that it's difficult nowadays to find copyrights that take more than 10 years to be monetized . Even the books that you mention took less than 10 years to reach a massive audience. And perhaps if the authors felt the pressure they 'd have produced even better works.