The Economist had a good article on this earlier this month. In short, for the past decade content creators have, for the most part, provided free content for Twitter, Facebook, etc. These companies in turn have made billions of dollars displaying ads alongside this free content. Sites like Substack are changing that and making it easier for content creators themselves to manage / monetize their content.
[1] https://econ.st/3fzbPKe (This is a "gift this article" link which I've not used before. Hopefully it lets you see it if you don't have an account.)
[2] https://www.economist.com/briefing/2021/05/08/the-new-rules-... (The article itself)
