For the majority of programmers I think it's lack of experience with data structures of any kind. C programmers have to understand pointers and most (I assume) would have implemented at the very least their own linked list at some point and maybe even a tree. But there are so many programmers who simply lack this experience so talk of pointers, links, graphs etc. is unfamiliar.

Then there are those whom I'm sure should have the necessary experience (because they are C programmers, for example), but still don't seem to get it. These people I think just don't care. They don't care about version control and therefore it's irrelevant what git is trying to represent. They just want to get their code merged.