Monica Dinculescu on web components and why we might care:
... before web components came around, you had to wait on all browsers to agree on a new element (like, a date picker). And even after they agreed on a new element, it took them yeaaaaars to implement it... With web components, web developers get to write such elements, so that you don't have to wait for 10 years before all browsers agree that they should implement a date picker.
I'm probably wrong in conflating the two, though. Even the React Docs say:
React and Web Components are built to solve different problems. Web Components provide strong encapsulation for reusable components, while React provides a declarative library that keeps the DOM in sync with your data. The two goals are complementary.