Having a successful social space does not necessitate, and I'd argue precludes, having a universal audience of everyone.
Also, you are currently on what would qualify as a social network, and between HN, Mastodon, and choice tech subreddits like I find myself well inundated with social forums to talk about stuff on. Thats even precluding how Github and Gitlab have turned into faux social networks around projects, how IRC and Matrix exist as real time chat options, etc.
There's still an ongoing webcomic (A Tale of Two Rulers) that's a world where Zelda and Gannon choose to marry instead of war on tumblr. It's incredibly awesome and part of what I'm on tumblr for.