It is because the primary target for markdown is what would in any other formatting language be the source. Markdown has no source. It is guidelines for good looking plain text layout that when followed can be used to make a typeset document.
Everybody sort of knows it sucks as a formatting language. But we love it anyway. The benefit of being able to get a typeset document from a nice looking plaintext document is just too convenient. It is why specialized markdown editors make no sense to me. Why would you target something as shitty as markdown if you have a specialized editor? But really, if you at all care about the semantics of your document don't write it in markdown. But more importantly please don't kill the utility of markdown by adding semantics to it, all that noise just make the plain text look bad.
Everybody sort of knows it sucks as a formatting language. But we love it anyway. The benefit of being able to get a typeset document from a nice looking plaintext document is just too convenient. It is why specialized markdown editors make no sense to me. Why would you target something as shitty as markdown if you have a specialized editor? But really, if you at all care about the semantics of your document don't write it in markdown. But more importantly please don't kill the utility of markdown by adding semantics to it, all that noise just make the plain text look bad.