It makes vastly more sense to transmit a patch attached to the specific code base state that it is intended to modify: in other words a patch doesn't exist in isolation. Git is great; I'm not saying everyone should use any particular Git-hosting or code review framework. But the fact that the inventor of Git continues to use email in one particular project with many expert and experienced contributors has more to do with their expertise and experience (aka age) than with the benefits of email. I mean look at the reality of these people's workflows: they're using things like Mutt and Gnus to read email locally and apply patches from local email. I get it, I've done it, I've even run a local dovecot for the purpose. It had it's time in technological history. That time isn't now.
There are multiple open source projects that I would have contributed to were it not for the email-based flows (e.g. emacs).