In economics, a network effect (also called network externality or demand-side economies of scale) is the phenomenon by which the value or utility a user derives from a good or service depends on the number of users of compatible products. Network effects are typically positive feedback systems, resulting in users deriving more and more value from a product as more users join the same network.
The value of Twitter and Substack isn't the HTML or the CSS, it's the social circle behind it. That's why Facebook, founded as a Harvard social media site, outpaced Friendster and MySpace. That's why half your current crop of comedians and media pundits came out of the Ivy League. That's why The Federalist Society exists.
Like, by all means, make a new BlueSky or Mastodon or Lemmy whatever. Thank you. But "What if we had a new Facebook, for annoying marketing dweebs?" it's how we got LinkedIn. And a thousand other knock offs of LinkedIn.
So, keep that in mind.