Interesting, I wouldn't think that would be a common use case. Were the websites totally static, or were they inside of another app that actually handled the dynamic bits?
React is good for completely static sites. ReactDOMServer.renderToStaticMarkup() is a lovely way to use components to orchestrate a static site even if you need data from external sources using Flux or alt.js or something. If you know React well you can do anything you'd do in Jekyll or Hexo quite easily.