Maybe it's just me, but I don't pay much attention to the github issue list unless I'm actually working on the MonoGame source code. I guess I consider github to be where the source code lives. So, yeah, I dunno. Maybe it's just not clear to the community how things are supposed to work around here.
As for the documentation on the website, yes it's prominent, but if you want people to help I think they need to be asked directly. As it stands the first page of the documentation says it's a work in progress which kind of implies someone else is doing it.
If it was me I would do this:
We need help writing the MonoGame documentation!
As you know, documentation is what separates good open source projects from forgotten ones and as it stand the MonoGame documentation is only a little way to being great. If we all band together, we can make it great!
This is call out to all MonoGame developers willing to help if you have tutorials, code snippets, experience with the various platforms, youtube videos or any other form of documentation. Let's gather it all together in one place and make MonoGame even better.
Followed by instructions on how to contribute...