maybe they are reading the DM to scan for threads which MNHQ might need to pull, in a kind of 'monitoring' role?
So shutting the stable door after the horse has bolted then!
What about if you copied most of the book in large chunks to use for commercial gain? Some of the DM "articles" seem to consist mostly of copied material.
The article can consist largely of copied material, as long as they are using it to discuss or review it. Most of the DM articles don't actually use large portions of the threads, they just copy key posts from very long threads.
If everything on the internet is "in the public domain" and can be used for any purpose by anyone, then why are there any copyright notices on any website?
No it's not a free for all. Copyright is still very important. "Fair Use" is a term within Copyright that allows portions of copyrighted material to be used in some circumstances. That includes this kind of DM article where the content is discussed. They couldn't just copy an entire page from MN and post it on its own.
YouTube has had to deal with a lot of similar issues where people post their own (copyrighted) material, then someone else posts a video that reacts to it. The copier is allowed to show large portions of the original video as part of their video, as long as they are discussing the original. They cannot just post their own copy of someone else's video - that would get removed as a copyright breach.