A lot of those "guests" are people who find public GOC posts through web searches.
Over the years, I've gone back and found my old posts simply by Googling topics I posted about before.
That's one way for a forum like this to grow - by having good, public content that's easily search engine optimized.
The downside is anyone can find it, theoretically.
The upside is most people who find it will find it based on topics that they can find through a google search and a lot of the traffic will be focused on that content to begin with.
I stumbled upon an ANTIFA forum that is also public a few months ago but I doubt that anyone here would be able to find simply because the odds of most people here searching for easily search topics that those people talk about is quite low.
Also I was doing some very advanced hackery to find them... it's seriously like going into the twilight zone seeing what some of those guys talk about. They talk a lot about the same sort of gun related stuff we talk about, but then they go on Doxxing witch hunts, reputation and career assassination, coordinate boycotts with leftists political groups, and of course, organize riots... it's REALLY creepy.
I'm pretty sure the site operator here know which forums get the most traffic and keep those open for search indexing. It's a good strategy to promote growth.
A good way to make money is to have private forums that are only accessible to logged in members OR that can only be found by sharing links. Both have different use cases that can be used to generate growth, revenue, and community.
Interestingly, YouTube does this too. There's 4 different states for YouTube videos from monetized partners: Public, Private, Unlisted, and Membership. Public is optimized for Google / YouTube search. Private and Membership are by creator invitation only, and unlisted is by shared link only.
This is how web content naturally organizes itself into surface / deep web layers of the internet.
Interesting to know is that content can be both public and deep web. It all boils down to SEO. In that scenario, from a practical standpoint it's almost as good as being secured and unindexable by a search engine.