I'd argue that the reason a lot of developers have not learned git in depth is because it's actually kind of terrible from a UX standpoint (lots of inconsistent naming of things and somewhat leaky abstractions), and that Mercurial faced an uphill battle in large part because it lacked compatibility with what people were already using. I haven't used Mercurial, but from what I've heard quite a lot of how jj does things is similar to Mercurial, just in a way that's compatible with git. I haven't used git directly for over a year in favor of using jj despite exclusively using git repositories, and no one I've worked with has even needed to be aware.
> I'd argue that the reason a lot of developers have not learned git in depth is because it's actually kind of terrible from a UX standpoint
Not really. I remember my early years with git and the favt was that I never needed more than clone, add, commit, pull and push. While I’ve done some mistakes that got ne to learn more, especially with creating branches and undoing. I’ve never needed a lot, even when I started using GUI which exposed more concepts.
Why? Because I have no understanding of version management and how it’s useful in a dev workflow/release process. I was just using it for checking in work.
Since then, I’ve read the “Pro Git” book, learned how devs and teams handle versioning and devel a good understanding of how git can help me in my coding process and general software development. And it’s very good at what it does.