If this in true then why do so few projects use a mailing list nowadays instead of something like github.
>Every machine can do plaintext email.
Every machine can do web browsing too. More people have used a web browser on their computer than a dedicated email client (as opposed to a web app like gmail).
>As opposed to login into to a bespoke web interface
You have to log in to email too.
>mainly primarily designed to be friendly to novice users.
What's wrong with that? Having good UX is a win. The UX for creating a new repo on github is a million times better than creating a mailing list (yes I have set up a mailing list for a project I made and no one e ended up using it except for me. Meanwhile I had much more success with getting people to join and discuss the project via Discord)