Why use a third party social platform at all? They have a website.
There are 3489502983450896 open source forum/groups software packages for every platform, every language, every database. Same with authentication. Hell, they could even drop in OAuth so people could still use their FB credentials without giving all their users' data up.
Hosting their own groups is a less than a one day job. There is absolutely no excuse whatsoever for this decision. None.
