"Groups" (Facebook or otherwise) do not magically stay open. There has to be a moderator for them and "community values of the host" need to be maintained. It's THEIR orientations, as they own and host the situation. Might have become the target of spammers? Perhaps in need of a new moderator? Or perhaps the "traffic" decreased too much? Many possibilities.
Perhaps that one group disbanded and was re-invented under another name? I'm not on Facebook, so I don't know.
CBODY67