Maybe when brought back it was set not to let new members post just because most new members to any forum that doesn't have a test as a part of sign-up are spammers, where the first and only post is usually advertising. I've seen that a lot. Some people have given up operating forums because of it, and it's a lot of work to deal with it.
But that doesn't really explain why a lot of the old members are no longer posting. I guess they've lost interest in this forum or don't even know it's back in operation.