IMO the problem is size/scale. If you're too small, then you just have people going through the motions of talking to each other in an attempt to make the platform seem real so more people will join it. If you're too big, you won't be able to curate effectively. There's a sweet spot in the middle, you start heading up around only maybe 20 or 30 users (the point at which it becomes impractical for everyone to know everyone), and when it starts heading back down depends on the culture, but go down it will.