Plugin developers are at the whim of GitHub’s pricing model and privacy policy (something many of us who use Obsidian because of its “you own your data” model object to).
Whims of GitHub’s pricing model? It has been free for public repositories from day one and still is. What is the concern that doesn’t exist with the other three options you list?
And why would Azure be a better option when its the same company?
I’m all for people having more options but GitHub’s pricing model isn’t a concern at all and these other concerns you list aren’t any different for GitLab or Gitea in the future. I’m not sure why the Obsidian team has GitHub as a rule but its a better bet than most other options given its dominance and ownership by Microsoft.