the components should be reusable, not the styles on them.

Besides global font settings CSS nowadays is mostly used for positioning and isn't reusable.

For components, bundling the CSS makes sense. For other use cases external CSS resources with inheritance are very beneficial.See for example Scalable and Modular Architecture for CSS or any modern CSS framework for lots of examples.

reusing css is a great idea for websites, react and Vue are most commonly used for web app where the atomic unit of reusability is the component.