OK, but then I still have to do work to get that patch and integrate it into my existing systems.

I don't know if you've ever used GitHub, GitLab, or CodeBerg - but PRs just appear in a list there. I don't need to do any work. Very handy especially if they're big changes.

I can also leave comments on specific bits of code, rather than emailing someone.

But that's require a web browser, dealing with 2fa, and I would probably still export the patch and apply it locally to test. Using email can be done on a potato system, using my email client, which already have my workflow automated. Replying someone takes even less effort than commenting.