they declined, saying they could be more productive with React
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
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.