[codingdave]

Markdown is useful for editing, but completely irrelevant to reading. So there simply is no demand for such things. It also greatly limits formatting options compared to the editors that authors and publishers already have, so they would be adding restrictions to their own work by pursuing Markdown.

In general, Markdown's use case is for easy editing of basic formatting in simple documents. Perfect for notes and small bits of documentation. Not perfect for many other things.