Not wanting to dive deep inside the code but make a complicated website is like saying "I want to modify the engine of my car but I don't want to look under the hood a single time"
Well, I guess that works if you have a VW Beetle ;)
Well, hopefully an SSG is saving you time compared to just writing a quick crawler that saves each route of your local Express app into a deployable static folder.
If you find yourself credentializing in the source of an SSG because it turns out you're doing something it doesn't support, then there's a point where it might've been faster to build as a dynamic site (more general tooling) with a static site build step.
It's an easy place to find yourself since so many SSGs generalize around blogging.
Well, I guess that works if you have a VW Beetle ;)