I use the graph to see whose fork of a codebase is most up-to-date, or has potentially useful revisions not merged into the master. I've come across a few projects whose "master" repo is all but dead, and a dozen other people have continued development independently - sometimes having created duplicate bugfixes, etc.
Developers come and go (often without warning), so what I'd *really* like to see is an interface where the codebase is the focus, and no one user or team "owns" any kind of one-true-fork. All forks should be considered fundamentally equal, and judged on their individual merits (recent activity, most activity, most contributors, etc.).
And having issues, pull requests, etc. tied to one single fork is just wrong. If something affects the "main" fork, then it quite likely affects all the others, too, and those forks' maintainers should be allowed to accept or reject those items as it relates to their own fork.