Firstly, thank you for gathering all those resources!

I think roadmaps are more common in projects where there's a management hierarchy above the programmers, who don't do any of the programming themselves, and use them for communicating progress and expectations among others who are interested in progress although lack the technical understanding to read commits themselves.

In Bitcoin there are lots of non-technical folks interested, although there really isn't any official management layer between them and the programmers. It's a difficult situation because you could argue that developers are slowed down by the need to interface with non-technical folks themselves, although I think that's also important because it means the developers get a direct understanding of what the community thinks, and what the community does and doesn't understand. There is also the possibility that non-technical folks get interested in the details and improve their code literacy, although I imagine that demographic will always remain a minority.