This mattered because speed is the killer feature [1], and speed is often seen by users as a proxy for reliability [2].
[1]: https://bdickason.com/posts/speed-is-the-killer-feature/
I used Mercurial, professionally, back when there were a half-dozen serious VCS contenders, to contribute to projects that used it. I disliked it and found it unintuitive. I liked Git much better. Tastes vary.
Git made me feel like I was in control. Mercurial didn't.
Mercurial's handling of branches was focused on "one branch, one working directory", and made it hard to manage many branches within one working directory.
Mercurial's handling of branches also made it really painful to just have an arbitrary number of local experimental branches that I didn't immediately want to merge upstream. "Welcome to Mercurial, how can I merge your heads right now, you wanted to do that right now, right?"
Git's model of "a branch is just a pointer to a commit, commits internally have no idea what branch they're on" felt intuitive and comfortable.