That’s even more reason to consider it non-viable.
There is no reason to encourage or support this type of behavior in a project. It is their right to do with it as they please, but I’m not interested in a project that functions like this. The forks are continuing to operate like true community projects.
He doesn't owe those developers anything, of course, but likewise they do not owe him loyalty and thus since an open fork exists, his project will die.
Killing the project is also his right, but people also have a right to be upset by his passive aggressive behavior. Just announce that you're shutting down the project and move on, don't waste our time.
Users of the project can (and have been) moving to forks that are operated as open, community projects in the continued spirit of the project’s original intention.
For what it’s worth, the maintainer has stated their reasons and they are not related to AI or scraper bots.
I have no idea what that means other this person might not be the easier to work with, or get along with.
Some people get spam. Some people get spam about vulnerabilities that don't exist. And some people get threats.