Gwern is overly secretive of his privacy. I think it peaked when he showed up on a recent podcast but his voice and image were AI generated! And now his post is limited only to certain people. Elitism or paranoia?
It's difficult for us to know what reason they might have for anonymity until we know their identity, at which point it's too late.
Also, they've written many words across many years, in a time when "the internet is serious business" was just a meme. I suppose it is now.