> they can't because they are all stuck using React
You can get most—if not all—of that behavior in React with JSS and TypeScript. All of your component code (HTML, CSS, and JS) can be colocated in one file, you can jump to the CSS class definition, TS ensures the class name is legit, etc.
Svelte and Vue provide a more batteries-included experience, but React is very flexible.
But it's a far worse developer experience, particularly for designers and HTML/CSS/A11y folks who aren't as JS focused. It's not like you really are getting that much benefit from writing CSS in JS besides familiarity with a language you prefer. It's harder to read and parse at a glance (even for the devs who wrote it, I see this in practice all the time when pairing and attempting to fix layout and style issues with my devs), harder to inspect from the browser, encourages practices that undermine many of the core benefits of CSS, etc.
My whole point is that we should not be finding worse workarounds just so we can stick with the familiarity of React. Even outside of HTML and styling it is easier to do stuff in other frameworks than it is in React. React is not providing some magical level of power other frameworks don't provide.
I don't hate React, I'm just sick of it being the defacto standard. We are creating a React monoculture in web dev and it absolutely has secondary impacts on how we write markup, styles, and how approachable and accessible our codebases are. So many major decisions being made just so a team can stick with React.
Why not pick a different framework and get better performance, easier to write JS logic, easier to write and read markup and styles, and a code that designers and others can engage with easily without having to be JS fluent?
You can get most—if not all—of that behavior in React with JSS and TypeScript. All of your component code (HTML, CSS, and JS) can be colocated in one file, you can jump to the CSS class definition, TS ensures the class name is legit, etc.
Svelte and Vue provide a more batteries-included experience, but React is very flexible.