I’m not too bothered by the IRC, it is a bit annoying not being able to get messages/responses while away (unless you rig up something to stay connected), I haven’t tried the mailing lists yet (other than the ones used as part of the Guix patching process (which Guix does provide a nice UI for with issues.guix.gnu.org), but it was a real pain connecting git:send-email as a first time user for the send-email part. There is supposedly some new tool called Mumi, but I haven’t tried it yet.).

I don’t see what you mean about the IRC being a walled garden? It did take a bit more work to connect than registering for Reddit, but I’d say it is comparable to the effort of joining Lemmy (but without the nice persistence of Lemmy). Another reason they might have for not wanting to add more communication channels is maintainer fatigue, every communication channel they officially add has to be watched by someone; and if all their maintainers are comfortable with something else, they will have to take time out of their day (with them already likely being volunteers) to monitor the new channel.