Traditionally Next.JS isn't really a tool to develop a single page application (although you could CSR every page if you want to), since single page applications are... single page. These are all multi page full stack frameworks that make use of incremental static regeneration and hydration to have the best of both worlds.

We agree though, it's just a naming thing really. I make the distinction like this because traditionally a SPA can simply be served by a CDN since it's simply a single file, meanwhile all of these frameworks either require a server to render pages on request or prerender all the applicable pages and leave a few of them to totally client-side "render".

Also note how Vercel (at the time called Zeit, mostly known for Now) called Next.JS back in 2018 when they originally released it:

https://web.archive.org/web/20180628030830/https://nextjs.or...

   > Next.js is a lightweight framework for static and server‑rendered applications.