There are still a few groups left.
Why should you buy them? Because it's like buying a piece of real estate online. You pay once and get free traffic forever. Most groups are getting about 100 new members a week, so there will always be new faces to market your product. And unlike a website, you don't need to bother adding new content to it, or paying for domain, hosting or backlinks, you also don't need to promote them because all the SEO has been done for you and now they all get new members organically from Facebook recommending it and organic searches.
If you pay for ads or links there are many ways you could go wrong, but with these groups you pay once and own then forever, there are zero ongoing or maintenance costs and they are all set up so that you don't even need to approve the new members, posts or remove the scammers, because all the groups come with volunteer members who work for free to keep the groups clean just because they love you and they enjoy doing that kind of stuff fore free, forever.
Also unlike facebook pages, members are still shown any post with engagement in their home page feed and that drives even more traffic. And finally, a few of the groups have been making a consistent $20 to $50 for the last few years.
The remaining groups are employment and marketplace niche and the members in all of them are about 95% from the US, And finally here are a few screenshots with analytics of one of the groups:
