The problem with isolation of components is that then the stylesheets are no longer cascading -- each component needs to be re-designed to fit within a design framework, and there's no CSS reuse between components is entirely copy-and-paste. Good luck re-styling anything for "dark mode" without having to hand-visit each component's JavaScript and CSS.
Plus, component isolation has really slow polyfills. None of the Google stuff as of late runs on anything other than Chrome for like a year after launch because it's too slow and broken -- everything is being rewritten in Polymer, which relies on browser support for component isolation.
Plus, component isolation has really slow polyfills. None of the Google stuff as of late runs on anything other than Chrome for like a year after launch because it's too slow and broken -- everything is being rewritten in Polymer, which relies on browser support for component isolation.