I arrived at a similar conclusion, just from the other direction: It is really hard to get people to document. It is even harder to get those people to care a little bit about formatting.

Markdown is... limited, I acknowledge. But with a very small amount of learning, markdown is as fluent and simple to write as normal text. In fact, 90% of what I wrote before I knew markdown was valid and decently formatted markdown already.

If you asked people who don't document to document in rST or tex... then you'd have no documentation at all. Because that suddenly adds a lot of effort on top of what you want to write down.

Now for some customer-facing whitepapers and documentation, we do use rST. But there you have people who are tasked with paying some effort to create some decently looking docs. Not trying to coax developers into writing down some of their state of mind while doing stuff.