We don't remove defunct social groups because there's no easy way to do so. We did just remove a bunch of 1-member only groups.
We're limited by what the software does and supports, and if they don't include social group posts, well, there's nothing we can do about that unfortunately.
We have about a dozen "active" social groups. You can find them by going to the all groups list, then sort by Last Post date:
https://forums.psychcentral.com/groups/all.html