Maybe I missed it somewhere but what are these other platforms that users are creating successful communities on from scratch? Be nice to have a few live examples.
Primarily facebook groups and reddit. The one click join 'group' or 'subreddit' functionality of these makes it a piece of cake to start a community from scratch.
There's a few forums I used to to frequent where they tested facebook groups. Sometimes because a member decided to start one, then the forum admins felt they should have an official group presence, then the traffic shifted from the forum to facebook, then they never went back and the forum is now a graveyard in comparison to the facebook group activity. (one example is a wordpress community I'm a member of)
Some of these groups now have 10, 20, 30, 40k+ members. (Quite a few auto groups are this big, Tesla and some others)
It's not an all or nothing, black and white differentiation though. Many forums aren't completely dead or shut down because of these, but their activity is massively cannibalised by their members stretching their time too thinly between all these different platforms, trying to eek the best features out of each one and trying to make sure what content they post gets seen and engaged with by the most users. Guess which platform wins for that? Facebook, because they shove the content from other members you interact with into your feed, into your notifications, pushed to your phone.
Not that this is always a good thing, but it gets posters the most feedback, quicker than if they shared it on any other platform, so they post there first, and often only there.
Even phone messaging apps are cannibalising forum activity now. What'sApp group chats, as basic as they are, after all they're just a single threaded conversation, work incredibly well for small groups. Half the activity from one of my small gaming clan sites is us just 20 of us shooting the breeze in What's App now when we don't feel the need to create a specific topic on the forum.
Why? It's instant, it's mobile, it has push and we can easily share photos and videos. Now you can get 256 users in a single group chat.
Why you'd really want to do that, I'm not to sure, I'm guessing that would get a bit manic. But, if you want to create a small community to directly connected to every members pocket, for free, in seconds, with reliable service and rich features, then it's a no brainer.
Same with facebook messenger group chat, I'm in some large group chats that I pop my head in from time to time. I'd say 100 people in a group chat is still a community, even though it's a very informal one. When I want an answer quickly, I can post in there and get responses in seconds.
If they outgrow that then they'll make a facebook group, still free, still great features, speed and UI, but you have threaded conversations.
Who is going to spend the time these days to drop $200 on the bare minimum to get a brand new forum community off the ground when you've got all this functionality for free elsewhere? The answer is fewer and fewer people.
It's the communities and facebook groups that make it to tens of thousands of members that I then see considering the return to a more structured forum format. When it makes sense to have a way to organise and filter the content.
Facebook sees this explosive growth in groups and local communities, users are logging onto facebook less often to post status updates, and more often to check in on and engage with the communities on there. Mark has made it clear that community is at the heart of facebook going forward:
(This articles is ludicrously long, but you can get the gist, community...community...community...)
https://www.facebook.com/notes/mark-zuckerberg/building-global-community/10154544292806634/
They are going to be pushing community and groups hard going forward. I would not be surprised if facebook puts a massive emphasis into fleshing out and adding features to groups over the next 12 months. In order to stop these much larger incredibly active groups from migrating away from the platform they will need additional functionality to manage the huge amount of activity.
It does concern me that if they do start to do this, even doing something as simple as allowing the creation of nodes in groups for categorising content, then it will be harder and harder for these groups to migrate to a self hosted forum where the admin has the ability to monetize or add any custom non-facebook sanctioned features, as even the 'basic' facebook features and ease of use just won't be there and the members won't follow. (Basic features such as push, video upload, event creation, being able to invite members to events - features that help cultivate real life communities off line).