Unfortunately, the internet has devolved in the past few decades from a repository of variously-inclined content builders into a comparatively fewer set of monolithic semi-walled gardens.
To that end, SEO requires an ever-increasingly complex set of trivia regarding a few aspects:
1. The social media networks most likely to favor outbound links to your domain (pro tip: they all favor inbound links to their domain, then typically domains of other monolithic semi-walled gardens). 2. The means to gain traction in each of those semi-walled gardens, which varies heavily by domain, but effective distills to stuffing the magical set of keywords and hashtags at the correct timing. 3. The precise set of keywords on the site itself. They must strike a delicate balance between creating an easy x-ref to their social media presence, but also human-readable enough that people will navigate through a few pages (and therefore not adversely hurt the bounce rate).
I'm absolutely sure I'm missing a few details, but that's the general gist of the SEO business from my own deep dives.