Usenet was sorta like Reddit or other threaded forum sites but decentralized.
The word for “sub”, “forum”, “community” on Usenet was called a “newsgroup” or just a “group”.
Each server decided which group it should carry. News servers were mostly ran by ISPs. Back then, ISPs would have email service, you might get a home page on the web, and you’d get Usenet access via one server.
You could only post to groups that your own server carried.
Let’s say there’s a group about knitting (free.uk.knitting perhaps) and it’s carried by 40 servers. That means each of those servers would have to copy over every single post every single day. Don’t worry, they didn’t have to poll, it was UUCP which is push based just like Fedi is today, but still! Holy redundancy, Batman!
That collapsed once people were posting binaries, both because they couldn’t handle transfering gigs of binaries across thousands of hosts (already back in 1983 (yes, that’s 83, not 93) there were over 500 servers) and because they didn’t want legal responsibility for those binaries.
Usenet was the anti-BitTorrent. BitTorrent is efficiently letting people share small parts and pieces of binaries and piece them together, it’s the opposite of redundancy. Usenet, on the other hand, was redundancy city. And flaky as all heck redundancy with a lot of posts missing and threads being read out of order and laggily and buggily and it just didn’t work very well. (And the comparison to Reddit unfortunately also extends to the toxicity on a social level.)
A lot of Fedi’s struggles both early on and today come from this idea that every server should carry every post, which just doesn’t work. That’s also why hashtags on Fedi aren’t a good idea.
It doesn’t work technically and it’s inhuman socially. Ebba Grön has a song about it, “Mental Istid” which means “Mental Ice Age”. It’s all about one long algorithmic timeline where you can’t cry, you can’t sob, nothing matters, everything is homogenous, our lives are rapidly flittering past on status updates. That is what Twitter is. That is where the “Usenet-glob” model of Mastodon was heading.
The Fediverse should not try to be like Usenet. It should be like email. FEP-1b12 is more akin to mailing lists (and there can be separate lists on the same topic) whereas hashtags try to be Usenet groups or IRC channels and depend on an UUCP redundancy that just isn’t scalable or healthy.
A mailing list that’s mirrored across a couple of servers to distribute load isn’t a wholly bad thing. I’m not trying to completly write off all of UUCP and NNTP, there were historical reasons why it made sense given the bandwith limitations of the time.
But my main point is that “everyone needs to carry everything” is inherently a broken model. “The whole known network” tab on Mastodon is not your friend.