Once it was possible to set up discussion lists (or similar forums) that would, eventually, and essentially become self-sustaining, and fairly self regulating. Many such professional groups (which were for sharing and learning) emerged and ran successfully for a number of years. HRNET, for example ran successfully without almost any leadership or tending. Others, also.
But that was then, and what it takes to open and run a forum, or professional list, has changed. An online community needs far more nurturing and gardening than it did before. When they die, it’s not because the format is outdated, but it’s because what worked before no longer works. If you run a learning community, you need to lead, and you need to garden.