Static sites sit on a large spectrum from very simple to very complex. The nice thing about React is it works very well on very simple sites as well as very complex sites. So yes, for a very simple 5-10 pages site, using React might seem silly but for a site with complex theming and lots of clientside JS, using React makes things a ton easier.
React is a good paradigm to build UI. That's why people like it and use it more and more. If people both like React and need to create lightweight websites, why won't you let them do it?