I only have to sign up to Github once, not once per project.

Personally, it's not. I'm using GitHub and I also sometimes send patches in emails.

I'm asking specifically what part of subscribing to mailing lists is the tricky part, as that's what parent mentioned. I'm not saying it's easier/harder than GitHub's workflow.

I think you meant “how is signing up for GitHub harder than that?”

That's a battle??

This sounds like hyperbolic brought on by dislike, not a real indicator of time cost/effort. You've already spent more time complaining, than the work done to do these things!

That's how mailing lists should work.

Many mailing lists today reject posts from non-subscribers.

Of those that allow posts from non-subscribers, you will find that many are configured such that you will not get a reply, due to "reply-to munging". Your message will go to the list, but with a Reply-to: header designating that list, instead of (or in addition to) setting the more modern mailing-list-related headers.

Reply-to-all isn't a list policy; it's a behavior of the individuals. Some people don't reply to all. They think they are, but only the post author gets their reply. That is one of the motivations behind the Reply-to.

https://marc.merlins.org/netrants/reply-to-still-harmful.htm...

The CC part is highly conflicted. Most maintainers hate double emails, whilst some loudly insist to be CC'd, esp. the Linux kernel folks. So you need to read beforehand the preferred etiquette. And nevertheless, the tone on mailinglists is entirely different (and mostly extremely childish and unprofessional) than on ticket trackers.