I think we are talking specifically about server side rendering, which is a subset of server side functionality covered by a wide range of languages and frameworks, some of which predate things like node.js by quite some time, Like php, which literally started out as a server side template rendering language end of last century. Php and Javascript emerged around the same time if I remember correctly. I never was a big fan but it remains extremely popular and still runs quite large part of the web.

I'm not super opinionated on what people pick other than advising to not get tunnel vision and only consider one language. Also, static code generation and server side rendering are two very different beasts. Server side rendering of course can be as simple as just a static code generator where you don't actually persist the output (i.e. it's dynamic). But usually there's a bit more to it and you get server side views, caching, and a whole lot of other stuff that people forget about that is actually needed in a server application such as logging, database and other middleware integration, authorization and authentication, etc. Once you figure out you need all of that, a "lightweight" framework that isn't particularly good at any of that might not be the obvious first choice.

It's why javascript is much less of a mainstream choice on servers than it is in browsers. Yes you can use it and lots of people obviously do. But there are countless other very mature and well established technologies that you can choose from as well. And most of those can do server side rendering pretty easily as well as it is not that big of a deal to actually implement. If you need it.

I think the specific attraction of javascript based frameworks for frontend developers exploring getting into backend functionality is that they can use the same tools and frameworks that they were already using client side. Specifically react users seem to be looking for ways to use react on servers.