I used to be a member of 3 model car forums, which were good for advice of upcoming models, buy / swap / sell, and general discussion.
2 of them (Biante and Trax) shut abruptly because the companies ( not forums ) changed hands, and went to a completely different site, making the old site and associated info non-existant, and the last remaining forum (ClassicCarletables) still exists in a zombie state, as the owners refuse to respond to questions, which leads to member disinterest and inactivity.