So contrary to all other changes, this one was not done for Facebook to use. What was the reason behind RSC then?
If you watch the various talks and articles done by the React team for the last 8 years, the general themes are around trying to improve page loading and data fetching experience.
Former React team member Dan Abramov did a whole series of posts earlier this year with differently-focused explanations of how to grok RSCs: "customizable Backend for Frontend", "avoiding unnecessary roundtrips", etc:
Conceptually, the one-liner Dan came up with that I liked is "extending React's component model to the server". It's still parent components passing props to child components, "just" spread across multiple computers.