Another reason I host my own articles is that Medium is very heavy to load. Yes their design is great, but it's something that is achievable with a very small amount of CSS. This might not matter for a lot of people but I don't like how slow their platform is.
Is it? I had to write a bunch of µBlock and usercss rules to make their articles somewhat readable. The sticky bars waste a lot of screen estate. Firefox reader mode (Ctrl+Alt+R) is a wonderful thing, but it breaks on some pages (I guess due to Medium's incompetence or brain-dead priorities since they're still using gist for code snippets (every single snippet in a separate iframe!) instead of spending half an hour to integrate highlight.js)