Yes and now. Certainly not J.K. Rowling. She gets millions for whatever she writes. With steem, even if very successful, it's a few thousands. Let's say a book has 20 chapters and each posting gets $500. That's $10.000 - great for a small writer, so we see that happening. But very bad deal for J.K. Rowling, so we will not see that in the near future ^^
Additionally, everyone can read for free what is being published on the steem blockchain. But only members with Steem Power can upvote.
A third factor might be, a posting can only be monetized for 7 days. After that there is no money to be made by the authors.