Sorry I don't have the definitive answer on this, but I'm sure someone from the "Towers" will be along shortly. Some of the private forums have been dormant for quite some time, and it was generally felt that if the service was being provided elsewhere, or it was not being utilized then it was not worth providing the facility on PPRuNe. The first post in the thread probably gives a guide. I understood that there would be a warning posted in dormant forums and continued non utilization would probably result in removal.