The failing of many reminiscences of Usenet is that they're entirely or largely from a user perspective. What's forgotten is that someone needed to host newsgroups, and that that prospect became increasingly untenable.

Usenet died a death of a thousand cuts, though I'd argue four were the deepest and most lethal:

1. It got spammed to death.

2. It lost control over its culture, and that culture was crucial to its functioning.

3. It was too problematic for ISPs (or others) to provide ready access to it: spam, harassment, child pornography, and copyright violations all posed massive concerns.

4. There was no viable business model for providing the service.

See: <https://old.reddit.com/r/dredmorbius/comments/3c3xyu/why_use...>

All of those are significant, but I would (and did) argue that points 3 & 4 were the final nails in the coffin. Anti-spam measures and tightly-curated / moderated newsgroups could survive despite the spam, but with firms willing to brave the very real legal and financial risks, and without any other viable financial support, Usenet fell to a mix of mailing lists and early online blogging / forum software (phpBB, Slashdot, and others).

There've been several attempts to revise or update Usnet (most notably Usenet II),. Those ... have also failed to take hold. (Though in fairness: social media is extremely fickle, many apparently well-structured, and occasionally well-capitalised, attempts have similarly foundered, and the limelite often moves on with time.) Gaining traction and viability is a mix of luck, timing, and execution (mostly getting out of your own way).

Reddit can be seen as a response to points 1, 3, and 4. Reddit offers reasonably good spam defences, it has evolved protections against legally-problematic content (with some large bumps along the way), and it's attempting to develop advertising as a business angle. And has had some success at all of these.

There were other factors as well. One of the more significant, and a challenge for any client-mediated (as opposed to server-based) protocol is that different client behaviours matter and may give rise to incompatibiilties.

Where I witnessed this most glaringly was in email. During the 1990s I participated in a technical discussion where participants joined from Unix, Vax, Mainframe, and PC systems (and possibly others). Simple reply-acknowledgement and quoting practices differed widely and often clashed badly. I don't recall if Microsoft's email platform at the time (this pre-dated Outlook) clashed with Unix conventions, but hot holy hell did IBM's Lotus Notes Mail. And it was Annoying As Heck.

Usenet ... didn't seem to get bitten by this too badly, or at least not until Web-based gateways to Usenet became commonplace. Though, come to think of it, email gateways also existed, and that mailing list was mirrored to a Usenet group, so yeah...

The other factor of course was the emergence of more centralised alternatives, almost all Web based, to Usenet. By the late 1990s, phpBB and similar online fora were becoming the centre of discussions, and community sites such as Slashdot emerged. Those in significant part acted on the user-side of the equation. Where Usenet itself was increasingly a wasteland and feeds were hard to find, Web fora were easy, no-installation (the first SaaS models), and contained noxious behaviours far more effectively.

But the real focus is on the business case: if there's no profit, and unlimited downside risk, commercial enterprise will flee, at which point widespread usage becomes highly improbable. Distributed protocols and networks (Mastodon, the Fediverse, etc.) should keep this in mind. A possible alternative is to follow Usenet's initial foundation: independent institutions (e.g., higher education), but that seems at best a limited and niche category.