I tend to think the ecosystem is vastly dominated by established solutions. In order for a New Thing to win, it needs to be at least an order of magnitude better and more usable, or the network effect obliterates it.
Could it also be that social media sites depend on commingling “daily active users” vs “number of unique humans” for having high numbers? A web of trust would establish one live person per account, somewhat like Facebook had a policy for.