I guess they like markdown precisely because you can open it in Notepad on a Windows 98 or whatever, read and edit to your hearts desire, and then save it and be on your way. Maybe they find that presenting it as something a little more user friendly runs the risk of at some point running into conflict with that level of portability.
It's hard to understand the things people around here feel strongly about. I would certainly enjoy being able to send a markdown file to my colleagues instead of having to convert whatever note I'm taking into docx so that they can understand what a headline is. Even odt is not a real option as they'll introduce track changes or whatever in word and I won't be able to see the same document they sent me.