It takes a ton of work to run a forum. In the case of the two examples I linked, there's simply no alternative on Reddit, so it's not an option to use Reddit. Those communities are vastly more knowledgeable, organized, kind, fairly moderated, etc, compared to r/privacy.

I guess you get what you put into it in terms of community.

I used to be more interested in succulents. It's a shame mine have to stay under grow lights to not stretch out. It would be cool to have them scattered around...

I could see succulents benefiting from a Discourse forum, but Reddit likely does the job pretty well with photo sharing. The nice thing about Discourse is, I feel like threads are more permanent.

A forum I would want is a modern cooking forum for homecooks with a slight focus on science. Although I have not actually searched for one. It comes up on HN from time to time.