It doesn't solve the same problem as a static site builder. e.g. A static site builder lets you build templates using whatever plain html/css you want, and then you can write individual pages in markdown and have them generated using your template.

I think this is the way to go if you're not one to change the HTML very frequently. It can be a repetitive process to update HTML for each page if you've wound up with lots of them. If that's not so much a concern, go for it!

It’s fine until you have a list of blog posts etc that you want to generate your static site from

How is that different than just copy pasting a new page?

If you want the pages to share a header, footer, and menu, it can be a pain because if you ever want to change something in a shared component, you'd have to do it for every single page.

What if you want to update the template? You'd need to change it on every page. That's fine if it's only a dozen, but does not scale well.

I used to have a 5 page portfolio site and it was a pain even with that few copy/pastes to do in order to update my header. Static site generators ftw.