A book in the public domain can be sold, so probably by selling books. Or other jobs. This seems really interesting to me as someone who does not write books full time.
They established early copyright because publishers would just print copies of books and never pay the authors at all. The middlemen aren't going to do it voluntarily, and if they do, they'll be undercut by those that don't.
Authors can sell their own books even if someone else publishes it. Especially if it's published into the public domain.
And someone else can take the content and print it and sell it themselves
Wouldn't that be neat :-)
not if they sell or exclusively license the copyright to someone else.
Which is not the case for books in the public domain.