[err4nt]

HTML is supported natively in the browser, and custom HTML elements and their properties work at the same level as all other HTML elements as far as JavaScript, DOM, and dev tools are concerned.

React, while it may provide similar functionality to the programmer, is not natively understood, and while it can run in browsers, the 'components' in React are not handled in the same way in the browser as native HTML elements, JavaScript and its APIs don't know about them as HTML elements, DOM isn't aware of them (only their parts), and dev tools can't offer much insight because the app that's running is an unpredictable black-box to the browser.