I don't really agree, but also don't have a better explanation. Moderation and clients would have been solved, had Usenet continued to be huge. Email have had it's fair share of problems, including spam, but has always managed to survive because nothing has been able to replace it and it's still valuable. You could argue that development of attractive clients have died down in the past decade for email as well. Panic kept their Unison client alive for way longer than they needed to, and that looked pretty.

Personally I would love to see Usenet replace localized Facebook groups. It seems like every small town have a Facebook group, and if you have no presents on Facebook, you get no information. Usenet would be a perfect fit, no central authority to monetize and control the group, you'd be able to read about activities in your neighborhood, while having no account or an account with an organisation you trust.

The ISPs might not want to pick up the tab for running the servers, but they kept doing it for years after Usenet became a ghost town.