Many eyeballs better than one.
Even GCHQ combined with the NSA don't have enough engineers to peer review stuff they've made in house to make it better as fast as they want. There's a good chance other players interested in analysis of large graphs may want to add features which scratch their itch. Years ago this cost arguably would have concerned making it slightly easier to guess how GCHQ process graph data and that kind of argument would have restricted disclosure. Nowadays GCHQ's interest in relationships mappable as graph data is hardly a well-kept secret. Tor and SELinux have similar histories of being government funded security related projects for which development overheads could productively be shared.
Biting the hand that feeds IT
