alt Hacker NewsBut it is portable. It is essentially markdown files. You can download your repo, compile the Jekyll to static pages and publish them anywhere.
When you publish to Facebook, WordPress etc you can't easily get your stuff out. You will have to process them even if they allow you to download your content as a zip folder. The images will be broken. Links between pages won't work etc.
Facebook provides a data export service which gives you a zip file with a web version of all your content. I’m not sure what the difference is then between that and a Github hosted repository of all your content as a webpage.