Basically they become a target for spammers and seem to have lost most of their value.
There have been a few electronic discussion systems around like the BBS'es (Bulletin Board Systems) of old (that you dialed in via a modem through the phone line), Listservers (mailing lists that you had to subscribe to and everyone got copies of other people's responses) but one of the the oldest is
Usenet - it is like a BBS or forum as it's threaded but it's also anonymous - which is why it has died, i would guess. Follow the link below to see what they look like these days.
What you are using now to read this right now takes ideas from all those different systems and is the current state-of-the-art.
I never used Usenet but it's as "old as the web" sort of (cicra 1980) because i was never interested ... don't know why tho'.
Anyway, I found an index/FAQ to those old groups that came before us so if you want an index to 3 of them, you will find them at:
http://www.faqs.org/faqs/drugs/BBS article:
https://www.theatlantic.com/technology/archive/2016/11/the-lost-civilization-of-dial-up-bulletin-board-systems/506465/Web-based BBS directory:
http://telnetbbsguide.com/