Yes. For all intents and purposes they went away. And there are mostly no equivalent discussion boards (beyond narrow mostly invite only mailing lists) that allow only the sort of people (for better or worse) who had access to the relatively early Internet. Some large companies, students and staff at elite universities, and so forth.
Mind you it wasn’t perfect. But people tended to be posting under their own names associated with institutions. And the masses were kept out if they were even aware.