GitHub pages is really just a hosting service for Jekyll. My website is getting close to the maximum size for GitHub pages anyway (the limit is only 1 GB). Medium is unworkable for too many reasons.
I started out writing my webpage in HTML, and if you dig around you can find my old GeoCities page, but plain HTML suffers from some problems that make it high-friction for posting frequent updates. So you start adding a simple templating system. Maybe at first it’s just a header and footer you stick on to every page. Then you start adding indexes so you don’t have to update index.html every time you write a blog post. Your plain HTML starts getting more and more complicated, and it starts relying on some kind of library of scripts which you are now maintaining.
That’s what happens if you dive straight into it and use whatever technology is simplest to understand. I think most people would be better off picking a static website generator, to be honest.
(Also: When I started posting content to my website, Jekyll didn’t exist.)