In my opinion, in not using JavaScript they are missing out on a really nice DX. This is the kind of app that could be highly optimized _despite_ using React or something similar. Knee-capping your hiring to Make A Point (tm) is silly.
I have yet to see a website that felt better to use after switching to React or similar. To me it always feels like a straight downgrade in UX. A site that felt nice and snappy suddenly becomes heavy and sluggish.