Although it sounds like a silly reason, compare the names themselves. I don’t even know how to pronounce “mercurial” without looking it up. The word doesn’t exactly roll off the tongue like git does. And then the command itself is “hg”. WTF is up with that? I mean, ha-ha we all get the joke, but was the program made for chemists? Unnecessarily clever. Don’t underestimate the extent to which a difficult/confusing name/brand can harm adoption.