What is it specific that you dont get ? I actually thought hg is conceptually simpler.
And hg to me has always felt BSD like, Git was Linux like. Unfortunately everything with BSD failed to gain any popularity. Including BSD license in itself. ( Yes I know Netflix are using it in their Edge Appliance )
Coming from git to hg, it was a step back in time to branches that can’t ever actually be deleted and bookmarks are... not obvious.
Can you actually create two bookmarks on your current commit and then move forward on just one? who knows? I never figured it out.
I might worry about a monoculture around a hosted service like github, but not git itself.
Or consider openssl since libressl came out. Yes it's possible that codebase improvements would have happened anyways, but having open source competition is great.
It obviously isn't 'factually' better - that's a matter of opinion not fact.
And in my experience, both Mercurial's model and UI is very over-complicated with far too many concepts. Git has a smaller number of simpler primitives and primitive operations. I think that makes the underlying model of Git better and that's why I prefer it.
As it stands, it's just a lot easier to use Git everywhere though, just so developers don't have to learn a new tool.
https://pijul.org/ is the only somewhat somewhat interesting alternative I know about, but it's implementation is in alpha territory, and development seems dead.
https://github.com/facebookexperimental/eden
Previous discussion https://news.ycombinator.com/item?id=23124095