Browsers have native, built-in components like <select>, <select multiple>, <input type="button">, <input type="date">, etc. Styling and behavior of those is self-contained, with a public API.

The idea behind web components was to provide a built-in way to build your own self-contained components - something people have been doing for a long time with tons of <div> elements. But it's always been a challenge because doing that well requires adopting some consistent approach (usually through a library) that builds its own mechanisms. And there are many different libraries, and they all have different approaches. Wouldn't it be better to provide a standard mechanism for defining custom components and abstracting their styling/behavior?

Web components and other modern web tech could eliminate the need for libraries like React to build complex web apps with custom controls.