Git made some design decisions that sacrifice usability for speed when you're dealing with a gigantic repository on the scale of the Linux kernel, which is what it was designed for.

I believe that git won out over mercurial for the same reason that small start ups choose systems and processes that are the same as those used by big players like Google, Facebook, Amazon, etc.

People should try to make design decisions and choose tools for the scale they're actually at. Not the scale they hope to be at some day.