The author isn't in control of the chrome around it. It becomes an advertisement for the proprietary service. You can slap Markdown through Pandoc and host stat

The author isn't in control of the chrome around it. It becomes an advertisement for the proprietary service. You can slap Markdown through Pandoc and host statically somewhere where you do control the the chrome. This is a similar objection to say Medium, but Medium authors aren't usually developers and don't have the know-how. GitHub has forked Markdown in a way that is incompatible with CommonMark, GitLab, etc. So the author might accidentally buy into that fork which there is no quality control for (just look at the lack of care put into their attempt at admonitions).