The UX philosophy is radically different. One presupposes that you understand a lot more of the underlying system. The other tries to focus on what it is what you want to do, as opposed to how.

Mercurial is less intimidating if you don't know much about internals. But tbh, when I use Mercurial I still find myself searching which command to do things. As a frequent power user, I find the Git CLI to be more useable.