> Both had superior user experience compared to git

Highly subjective.

Both Mercurial and Bazaar were plagued a long time by muddled branching and collaboration story. In hg there were the anonymous branches, multiple repos, bookmarks, all worked in different ways and their interactions were confusing. Bazaar I didn't use much but remember not understanding at all its branching model then, and didn't bother finding out.

Git won because it got many things right from the start, and was better than the competition.