Also, if I want to get the most performance out of the car, or do something nonstandard, I need to know about the energy extraction process in order to pick better fuel or to adjust timings in the engine. (Sure most people won't, but if you want to, it's nice to have the information available).
Git's documentation (from what I hear, anyway, I've barely used it outside the GitHub client) seems like it's written to say "Everyone using git is a programmer, so everyone using git wants to know about git's implementation details."
As someone who would rather have a handle on the basics (and 99% of use cases) before digging into that, google does a better job at explaining what things are for. Which works, but I really wouldn't mind having some canonical user-friendly documentation available instantly on my computer.