They sure can .. but I don't see anyone typing ten thousand words of markdown on Android phone :-) ..

On a Tablet maybe .. but longform writers normally have a workflow ..and they are kinda already sold on to their editors ..

Plus there are few things about longform content - the image that normally goes on top of the post .. multiple tags .. a summary ..

And then there are curations .. if you wanna link chapters of book in a Table ( of content ) ..

And then there are libraries for offline reading .. as in download a book kindle style ..