Usenet was attacked by the bottom-feeders of the Copyright Industry (RIAA, MPAA, etc) with the help of a New York state attorney general said to be on a mission to eliminate child porn. So the equivalent of stopping crank calls by tearing down all telephone lines was done.
I believe the word and idea "spam" also had its origins in the Usenet. "Spammers" were attacked virulently in the newsgroups. And with the decline of the Usenet, we now see the effects. Those web-based discussion forums that were talked about above which people pretend are replacements for the Usenet are now full of spam. In fact, the spam/ads are everywhere, often in font sizes larger than the forum discussion text, and mixed in with it and around it. It is as if the forum operator is intentionally trying to be misleading, and the practices of web-based discussion site providers is as bad as the worst of pornographers who use every trick in the book to get the unwary and even wary to download their malware (or they break your browser with the latest script exploits).
The Usenet will come back again because there is a need for a refuge away from both the clueless and those trying to make a buck on a click. It may even be called "Usenet 2.0" or whatever with a "m*r*ns not welcome" sign on the door.