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.