Never looking at git history is like, not reading comments or something. It's an incredibly valuable resource for understanding why the existing code is the way it is.
I can’t even imaging having a spec that fully answers anything like this; Microsoft tried for that level of detail but I found they couldn’t keep it up to date.
If a bug pops up, you'd want to know why some code exists and if the original premise of the code is as it should be or needs revision.
I think it's very rare that a developer receives all that information up front in a team. Eg. Old codebase, lost knowledge or people leaving.