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.

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.

Yeah, I can be grateful, it's like a big red warning color that the project members are gatekeepy and don't wish to keep up with the times.

Don't come crying when you can't find any contributors, it's your own undoing.