The reason Facebook is where it is now is that when it was novel there was a lot of engagement. But as the novelty wore off, it became clear that your friends were not going to be able to produce the amount of interesting content you’d need to stay engaged. Most people probably don’t have enough friends on FB making the problem worse. In addition, Facebook’s privacy model requiring a double opt-in friendship makes it hard to add more friends.

So they started to loosen things: you can follow others, posts can be public, your feed becomes a mix of posts in your network and friends posts, etc. Now it is resembling Reddit. Numbers go up!

That is to say: these pure friend social networks start off with the right intentions. But with a similar product and incentives, you’ll end up right around where Facebook is now. If you want a different outcome, you must start from a different place.