I don't think being too good is the reason it didn't beat git. I think Mercurial didn't beat git because it's only marginally better. Not nearly enough to overcome network effects, but also just not enough to make people move for personal use. It is always advertised as more intuitive, and it might be, but the list of "very intuitive verb commands" largely matches git for the most common actions.

In addition the different kinds of branches are confusing. Once you understand git branches they're simple. Once you understand Mercurial branches you understand just one of the branching models it offers. I believe "bookmarks" are the most similar to git branches, but good luck finding out about them from the website without already knowing they exist. Instead it tells you all about keeping around a bunch of copies of the source tree.