Once you're using React for a web app, the cognitive load is not that high to use it to blam out a site, too. And it need not be slow or heavy, either; the website I'm currently working on uses React for rendering (both server-side and not, but it took me about an hour to get server-side rendering working for something where the very minimal state is only presentational) and has about a 60KB-gzipped JavaScript+CSS+images bundle all-told. (Of that, React is 5KB. Woo?)

I could use Vue, but I'm already using and continuing to use React, and I'm good enough at (what isn't actually) my job (because I'm no frontend developer, this is just what I do on the side) to minimize its impact on end users.

I also use React for fully static sites via Gatsby, though I don't love it, and to quickly build HTML mail templates. Granted, the bigger value here for me is JSX rather than React, but for my use cases they're functionally the same thing, and I do think you can get a lot out of using it. Especially if elsewhere in the stack you're already undertaking more complexity with it.