Copyright doesnt exist only to prevent people from getting your books for free. It's also there to prevent other authors from using your story for their own - for example, this is (part of) what prevents Universal Studios from putting out their own Spider Man movie.
Now, arguably this has even worse consequences on culture than the banning of copying ebooks. Still, it complicates the expected cost of a book significantly, so replacing current copyright with your proposal would require some alternative for this case as well.
this is (part of) what prevents Universal Studios from putting out their own Spider Man movie.
It's not though. It's the trademark that prevents that. Copyright only prevents them from making a Spiderman movie based on a story that's already been written. Nothing prevents them from writing a new story about a guy that shoots sticky goo from his wrists, and making a movie out of that.
I guess that story wouldn't be considered canon. But canon also has nothing to do with copyright.
Now, arguably this has even worse consequences on culture than the banning of copying ebooks. Still, it complicates the expected cost of a book significantly, so replacing current copyright with your proposal would require some alternative for this case as well.