git log: why are --full-diff and --pickaxe-all separate options?

I just did this:

$ git log -p -- /some/path

And didn't get the full commit. I know about the --pickaxe-all option, so I optimistically tried:

$ git log -p --pickaxe-all -- /some/path

Which of course, does not do what I want. Eventually I found in the man page that I can do this:

$ git log -p --full-diff -- /some/path

But now I wonder why these are separate options. Is there any reason they shouldn't be unified?

Regardless, perhaps --pickaxe-all without -S and --full-diff without -p should be errors?

j.