As much as it pains me to say so, they're probably right. If they don't know how to make a static site, and they're familiar with something like Next, then they probably can go faster and just let the framework take care of building the assets.
I wish people still made static sites using boring tech but times have moved on, but honestly there isn't much difference in complexity between a NextJS static site and a Hugo or an 11ty static site.
Edit: And OP mentioned he suggested Hugo or some other solution which is miles behind tools in JS/TS world. Not to mention it is Python based and this team knew React
All it takes is to actually write the html that goes into a component, rather than the component. I don't see how any react dev wouldn't be able to do this.
Also, I, too, would rather use react. I'd rather be able to reuse components I already have or to make some to reuse later, and to keep the project organized in that way, plus future-proofing the project to a certain degree.