> why does liking a tweet re-render the entire screen?

They're probably using Redux, which has been the go-to for state management in React for nearly a decade. I've always been averse to it because it's implemented using contexts and triggers those full re-renders - it was designed during the class-based components era and relied on people actually implementing shouldComponentUpdate(), which isn't really a thing with modern function-based components.

If they were using modern hook-based state management like Zustand or Valtio, full rerenders wouldn't happen.