Just guessing, but I would say that's because "git" is only derogatory in British English, and wasn't popular (if even existent) in American English until it's use as the name of a DVCS.
* Andrew Tridgell is a git for reverse-engineering BitKeeper
* Larry McVoy is a git for throwing a tantrum and withdrawing free BitKeeper
* Linus is a git for blaming Trigdell as the cause of Larry's reaction
Personally I think they're all gits.
Get me the source code. I got the source code.
Git is almost like a slang word that means get or got.
Yeah in British English it means a stupid person, you useless git! Almost like Nimrod means stupid dimwitted person.
Perhaps more dialect than slang?
... and the quoting of Monty Python