I can only speculate, but considering that I've been doing a similar thing for 23 years now, my guess is that the work required to run and maintain that community site was just too much for the revenue (if any) that was generated.
When you start a site like that, you can have all sorts of grand visions to help people learn and become better. But as the site grows, it starts to become an administrative disaster. The members constantly want new features added, usernames changed, accounts deleted, etc. And we haven't even gotten into dealing with all of the moderation headaches like inappropriate posts, spammers, users fighting back and forth, and a whole slew of other people problems that occur when you bring a large group together.
So what starts out a labor of love to help people eventually turns into a huge burden of managing people. And unfortunately, not everyone who starts such a site is cut out to be a manager in that way.
And let's not even get started on all the technical requirements that continue to unfold as the site gets larger. More servers are required, which means more development, maintenance, and technical expertise is required as time goes on. And if a significant revenue stream was never baked in to start with, there's simply no resources to hire the personnel required to run the damn thing. So it's just easier to fold the whole thing up and move on to the next phase of life than it is to keep the operation running.
Again, that's just a guess on my part.
