You can easily branch mailing thread into multiple separate ones (happens regularly on gnu mailing lists for example). Compared to that, threading in all of the git forges sucks hard.
You can easily search for open issues, tag/label them, mange milestones, you know, project stuff. Plus you get a web interface that's a bit more user friendly than mailman's. You can see what's going on, how much open issues there are.
How hard it is to open N separate issues and link them to the original one? It's exactly as much effort as sending new emails.
There's also the IETF datatracker, and various sites cobbled together to show the mail threads (eg. https://mailarchive.ietf.org/arch/browse/acme/ ) and states of various RFCs. And basically to manage work.
Email is great, and it's enough for IETF workgroups, but it's just a communication channel, it's far from an efficient tool to organize (track, show, share, plan) work.
How hard it is to open N separate issues and link them to the original one? It's exactly as much effort as sending new emails.
TC39 uses GitHub: https://github.com/tc39/
There's also the IETF datatracker, and various sites cobbled together to show the mail threads (eg. https://mailarchive.ietf.org/arch/browse/acme/ ) and states of various RFCs. And basically to manage work.
Email is great, and it's enough for IETF workgroups, but it's just a communication channel, it's far from an efficient tool to organize (track, show, share, plan) work.