Some examples.
I’ve come across academic journals that allow you to post drafts pre-submission but a condition of acceptance is that you remove these before publication. But if these drafts were now CC-BY licensed, you can’t be sure you’ll have the power to do this. (In practice, you might get away with simply ignoring this, but that depends on your willingness to lie, and your willingness to do so in the context of a legally binding contract).
More generally, public sharing of drafts is pretty common in academia, but publishers often want exclusive commercial rights to use the material (at least for some period/without permission being sought). So a CC-BY license that allowed commercial use would preclude publication in some academic journals, in a way that posting to the forum previously would not have done. (Likewise with posting some already published papers, where exclusive commercial use has been granted to the publisher but non-commercial sharing is allowed).
Posting the first chapter of a fiction book might not preclude publisher interest in buying the book. But it might preclude publisher interest if doing so now means that the characters can be used for commercial gain by anyone. For example, the publisher might want the exclusive right to create action figures of the character. It’s at least unclear to me that this wouldn’t be undermined by the first chapter having been posted under a CC-BY license.
I guess as an academic and a writer, if I were forced to accept a CC-BY license I’d be much less likely to post things directly to the forum, because I wouldn’t want it to come back to bite me later, taking away some opportunity. (That said, I’m an infrequent poster in any case)
So it’s the fact that the license removes the ability to assign commercial exclusivity, involves assigning multiple rights at once (for example, in posting a story one would automatically give permission to create films based on that story, which might preclude some options), and takes away control of the material (which might be important if a publisher would later want the writer to remove it).
I’m glad you both enjoyed it. I’m fine with people translating it for non-commercial purposes, so please do feel free to do this. If you end up doing so then it would be great if you posted a link here so that people could find the translation more easily (and, assuming I remember at the time, I’ll edit the post to include links to the translations).