The single biggest issue was spam. Being largely unmoderated, it became flooded with garbage as the reach of the Internet expanded. Conversation moved to web based forums, which IMO had worse UI in il the early days, because there was more ability to moderate.
And not just traditional spam. There were active campaigns to "sporge" thousands of news groups with thousands of junk posts. Hipcrime is probably something that would return ghits.
Oh, man. This was pretty much the final straw for the couple of newsgroups that I loved dearly back in the day (rec.arts.books.tolkien and alt.fan.tolkien). The once-vibrant community was already atrophying (due largely to a lack of newcomers and the usual gradual attrition of old regulars), and then somewhere around 2006 or 2007 there was a massive sporge flood that got past spam filters and made the groups unusable for about half a year. Once that ended, very few people were left.
Well, sorta. Yeah, spam was a big problem. The other problem is that there WERE moderated groups, and the original intent when creating moderated groups was that moderators would act like adults. They largely did not, and even if they did, they were usually strongly opinionated and would moderate according to those opinions.
