(Almost) Nobody, sadly. I run a session weekly, and if I had the time, I'd redact all the scenarios and adventures I come up with, but actually prepping and running the game is already a lot of work. I'd have to work up my notes so that they are readable and runnable to a level I know I'm not going to be able to- and I suppose many SGs here feel the same way.
What we can do as a community is share chronicles of the sagas we play in. No need to be an SG, no need to write up anything professionally. Just sharing your experience of play and maybe if you are the player who narrated the adventure, ask for feedback.
I think if everyone with an ongoing saga makes just one of their players post and share what amazing game they're being part of, the community would get a huge boost. Sharing stories and encouraging mouth to mouth is what we can do.