I think the failing point with all(?) of the attempts in this space is that, to phrase it in a very handwavy pseudo graph way, “real world” social groups depend on people who are “hubs” with a disproportionately large number of links to individuals, the majority of whom have far fewer links comparatively. Communities are anchored by these “super friends”. Those are exactly the least likely people to ever consider using a site/app like the above, but the most important to have as they are the ones with the requisite initiative and/or social clout to actually "herd the cats".

Basically, the Friendship Paradox https://www.wikiwand.com/en/articles/Friendship_paradox