And they were big bandwidth sinks due to the distributed model usenet has, so it was easy for ISPs to yank the carpet and look at the immediate gains.
The massive cross-posting of troll threads in the late 90's is what helped kill it off. The lack of effective moderation controls is the biggest weakness of Usenet.
While this didn't help, I don't think it was a key factor for ISPs. Most ISP NNTP services didn't carry binary groups anyway for bandwidth cost reasons. There were some issues with groups that linked to where to find copyright covered material, but the RIAA and their ilk were going more for the direct sources at the time. The public list/pointer resources were actually useful to them as lists of places to chase down.
Of course this led to people paying for external NNTP services which did carry the binaries groups. These services were obvious targets for the RIAA and other such groups unlike the ISPs.
> they were big bandwidth sinks due to the distributed model usenet has
This was a far more important reason, even without carrying binaries groups Usenet could consume a large amount of bandwidth. As well as the incoming load, and the bandwidth used sending data to clients, back then modem access was common and NNTP lead to people leaving the line open to download a huge pile of stuff (most of which they'd discard without reading anyway) meaning ISPs would have to invest in more modem racks, impose unpopular limits, or be perpetually busy, any of which would lose them custom.
Another significant issue was the cost of building and maintaining the servers required too. To run an NNTP service for a noticeable amount of users with reasonable performance you needed an arrangement with impressive IO performance stats for the time, and the access patterns (constant & random) could be murderous to the drives, sometimes chewing through them as fast as they could be replaced.
Usenet died for the same reason Facebook won: people exploit "free" forums in ways that ruin the experience. It's simply not possible to have an unmoderated discussion environment in an unrestricted internet, which is why we're having this discussion on a moderated site.
What I think led to the decline was at least a combination of:
1) an overrun of SPAM - Usenet was first to be hit by the spam flood, email SPAM came later as Usenet usage died off.
2) the 'newness' factor and the 'new shiny object' factor of the web drew away existing users, and resulted in new users never joining (i.e., pictures, fancy formatting, etc. all made plain text character Usenet posts look "old-fashioned"). And once you have a situation where new users don't join, and some number of existing users continue to depart, you are on a downward slope to disappearance.
Both of the above helped contribute to ISP's dropping NNTP service. Bandwidth costs for #1 (plus bandwidth if they were carrying alt.binaries.*) and a drop in NNTP usage due to #2. They (ISPs) no longer saw offering NNTP as a sales factor for obtaining subscribers, and once NNTP was no longer a "hook" to bring in subscribers, it was only a matter of time before they decided to just drop it entirely.
And of course ISP's dropping NNTP accelerated the issues around #2 above.
[1] https://www.cnet.com/news/n-y-attorney-general-forces-isps-t...
I was a really late adopter to torrents because of my background in usenet, sometime around 2010 all the alt.binaries I used to frequent went dead or were broken with little par2 support.
It was a great time back in the early 2000s, though.
If I'm honest, I don't download as much as I used to, but I do miss the niche communities based on those groups, though. They have since moved to IRC but for the most part its all gone from what I can tell.
For any method of communication, you can transfer content that someone else tries to prevent.
You can mathematically prove atop Shannon's theorem that if the system can transmit comprehensible text information between two users, it can transmit binaries. Worst-case scenario, the users could use the text information layer to just say 'one, zero, one, one, zero, one' at each other, etc.
(Socially banning them can certainly "work," in the same sense that social banning works in any context: pushes it underground out of the moderators' lines of sight. Depending on what you're trying to accomplish, that can be good enough).
