(Yes, the astute among you will likely recognize I also posted this to Station. Congratulations!)
I've been thinking recently about the concept of "walled gardens" with regard to online spaces and something definitely clicked. Despite the fact that the Facebook guy used that term a while ago, it is sort of how the Internet was before the advent of the big "town squares," and it's how certain parts of it still work. Gemini and Gopher are a lot like this (though Gemini seems to have its "town squares," like Station and the BBS) and spaces like Telegram are as well, where channels link to channels which link to channels etc etc etc and most of it is utterly inaccessible from the surface.
The term "gopherhole" seems to allude to this, and this is why I'm not really including spaces like Matrix or Discord in this, as most of these spaces are simply just private and require invites, whereas one can somewhat freely navigate the walled gardens of other platforms.