Most Windows users, sadly, are simply too backward to use anything that isn't tightly integrated into the Microsoft ecosystem. So, it never really helped Mercurial that much.
GitHub, however, was what drove git.
Unfortunately, Github is to source control as PowerPoint is to presentations. It works--but it's a dumbed-down default and nobody thinks about the fact that there are sometimes much better alternatives for your use case.
Powerpoint is optimized for marketing and not much else. It exists because of two reasons:
1) Most people actively suck at presenting something. Forcing them to put their presentation in Powerpoint-standard forces some level of organization on them.
2) A lot of business presentation IS marketing--and Powerpoint is fine for that.
The problem is that a lot of technical communication really doesn't fit into Powerpoint-standard (see: space-shuttle disasters for example). The problem is that now nobody knows how to do anything else and never even thinks about doing anything else.
I'm a big fan of chalk talks for anything mathematical. I find it hard to stay engaged with slides, even if the presenter uses tricks like revealing one step at a time, annotations, etc.
This is a version control misfeature/bad practice.
It's almost the single version control system that has it as part of its regular commands (though others allow it, generally as part of an admin set of permissions and usually with super clear warnings not to do it).
And it's far from a reason why git won. Git won because it was written by Torvalds and every script kiddie dreams to be a Linux kernel hacker and because the Facebook for Code, Github, took off and it was based on git.
Heck, I'd "accuse" you of rewriting history right now :-))