As I said, that is arguably the reason. But I think we have passed the point where that is actually the reason now.
A group like that is looking to achieve a mission-oriented result, not just hang out with like-minded people. So convenience is a factor. But I know a few people who have set up Facebook groups this summer while being annoyed at Facebook, in the correct believe that that's where the people are.
It's different for other kinds of communities. E.g. a gaming community tends to set up a Discord group, and a programming language community, well... I'm no longer sure if there's a single "place" for those any more.
A group like that is looking to achieve a mission-oriented result, not just hang out with like-minded people. So convenience is a factor. But I know a few people who have set up Facebook groups this summer while being annoyed at Facebook, in the correct believe that that's where the people are.
It's different for other kinds of communities. E.g. a gaming community tends to set up a Discord group, and a programming language community, well... I'm no longer sure if there's a single "place" for those any more.