There was a long thread on the topic in the emacs-dev mailing list not too long ago that generated a heated discussion of over half-a-thousand messages (where most of it was around "the proper way of sending patches"). I'm not trying to start another flamewar.

The basic notion is that the email threads model is focused around the subject line, and PR-model is specifically designed to have discussions where the code changes take the main stage.

I'm sure if you ask Jonas Bernoulli, Steve Purcell, Oleh Krehel, Bozhidar Batsov, and many other prominent Emacs hackers, they'd probably agree, without PR-model, it would be a lot harder for them to find so many contributors for great Emacs packages they authored and maintain.

To be honest, it feels a bit ironic when the shepherds of Free Software (GNU hackers, et al.) choose to ignore the people's free will, and in 2020 it is clear - people have made their choice. They don't want to deal with email threads, patches, etc. The majority of developers prefer to be able to issue Pull-Requests instead.

But there's something else, there's now an entire generation of software developers who simply don't know how to deal with sending patches, etc., and they don't even care. And that's not a good trend. The issue of patches vs. pull-requests has become generational. And if the old software projects fail to adapt, I'm afraid they'd slowly start dying.