Technically it doesn't. Unless developers add a bunch of logic to run in JS after the page loads (e.g. React's useEffect), everything it needs to render should work just fine without JS enabled.

This is my biggest complaint with these supposedly static site generators.

The resulting sites are anything but static.

My biggest regret of 2020 so far is agreeing to use Gridsome for a site, promised by the docs and a dev that it was a static site with "only as much VueJS as was desired for additional functionality".

Yeah, I know now.