It's AA7BQ's servers. And his forums. It is a privately owned system. He can run them however he chooses.
If you don't like Fred's choices (and I'm not suggesting that you should), go elsewhere. There are many other places... like here.
Personally, I think it was a poor decision, and making some of the forums subscriber-only will backfire on them. But... my opinion wasn't asked, and it is his system.