I totally get your point, and i'm crossing fingers that the postmortem will include the keyword "google" or "gcp". I didn't see that tweet from Dane and its a nice reaction from him, but the user asked if it has something to do with google and he didn't answer, I just find this a bit frustrating, and maybe the postmortem will answer those questions. My whole point is that I don't care if CF relies on third parties, I would just want to know when they do.
I left Azure a few years ago, even though I had thousands in credits, because I had uptime issue all the time for frontends. When I make my decision on which cloud i'd like to go with, knowing they could eventualy depend on another provider I was very disappointed with could be great. (e.g: if CF relied on Azure for pages I would have not go with them)
As for the OSS software, in my own postmortem I do mention when I upgraded something and it broke to my customers because some are developpers/devops (using my APIs). When they read all that, they're always much more receptive, and they can also inform their colleagues or customers about what exactly happened instead of just saying "yeah it stopped working for some reason"