Say you want to contribute to a project and find out the only way to do so is by discussing the issue on IRC or the mailing list, then submitting the patch per email.
Mailing lists intimidate me but I haven’t ever tried to communicate by one. IRC is probably fine.
I’ll be honest though, I’m not going to submit a patch to a mailing list unless there are pretty clear and easy instructions. Forking a project and opening a pull request on whatever forge (like GitHub, GitLab, and others) is easy. I probably do it once every three months or so when I find a bug I know I can fix. Mailing lists are just enough trouble (with my current level of understanding) that I’m probably not going to do it.
I’ll give an example. I found a bug in the JDK that was fixed in 17 but not in 11 and I was trying to figure out how to report it or backport it myself. It was crazy the amount of hoops I needed to jump through and I gave up. I’m not saying the project should be different so it fits my needs or anything, I’m just using this as an example of hurdles discouraging me from contributing. I think the vast majority of devs are probably at the same place and don’t want to fool with mailing lists. (I’m not saying projects should stop using them.)
