I can answer that, since I also made a small static site generator from scratch in python.

I was using another static site generator (Hexo), but at some point I wanted to change some things and add some custom html to my posts. Since the documentation was ... well ... minimalistic on some aspects, I also spent some time looking at the source code. But at that point I was really wondering what benefit I still had from using that generator.

In the end, all a static site generator does is collecting some markdown or RST files, converting them to html and putting that into a template html file. And generating some lists (index page, RSS, ...) and some metadata for SEO. So it took me a single Saturday to make a working static site generator and now I can do anything I want without looking up documentation or source code, since it's my own dumpster fire :-)

Because my team has an easier time managing our simple code vs a new tool. Also we have a lot of custom components because we use our site to provide navigation for our apps, dashboards and docs. I couldn’t find a generator that would fit all those requirements.