I believe one of the problems there is an inaccessibility problem. Atleast for the mailing list.
Most mailing list archives lack fulltext search and a modern looking design (I'm not even asking for an SPA or anything JS, just a tiny bit of CSS could make a lot of difference).
It's also not as easy to onboard, integrate and host mailing lists.
Ideally a mailing list could be hosted with a few button clicks, people could join a mailing list like they join newsletters (instead of having to send an email to the mailing list application with some command in it) and people should be able to anonymously send emails.
Plus points if you can, optionally, manage emails like github issues and properly keep track of bug reports.
I'm not a big fan of mailing lists either, for the reasons you describe
What I do dislike though is, as Slack is invite only (the software is designed for "Teams" in workplaces, not public forums) you have to explicitly request access from the admins and this is often via the mailing lists.
The invite-only nature of slack is probably why I never spend any serious amount of time in any slack, though some other factors may play a role too considering I quite enjoy Discord (OSS discords never seem to replace any discussion board, only supplement it, plus discord has unlimited search)
I rarely see a big textbox on the top of the main page of any mailing list archive that says "Fulltext search" (and isn't totally crap). "NNTP Gateway" doesn't sound encouraging in that it is explained and available for the layperson to easily employ as search tool.
I'm actually of the opinion that it would have been better to have a NNTP server to host various newsgroups instead of having various mailing lists. This would have made it much easier to view previous messages posted to the group and would have made it much easier to browse by those who don't participate.
The disadvantage is that it would require one to create an account on another server instead of just using one's existing email account for communication.
As for explaining and availability, I believe the vast majority of people would use search engine to figure out what steps are involved once something like that is mentioned.
Most mailing list archives lack fulltext search and a modern looking design (I'm not even asking for an SPA or anything JS, just a tiny bit of CSS could make a lot of difference).
It's also not as easy to onboard, integrate and host mailing lists.
Ideally a mailing list could be hosted with a few button clicks, people could join a mailing list like they join newsletters (instead of having to send an email to the mailing list application with some command in it) and people should be able to anonymously send emails.
Plus points if you can, optionally, manage emails like github issues and properly keep track of bug reports.