Dev attached to the Bitbucket team here. While we love and support open source where we can, the vast majority of repositories on Bitbucket are private or public but maintained by a single organization. Our core focus is professional teams, which typically means branching (rather than forking) workflows. This has lead us to prioritize features like branch level permissions over network graphs and other features focused on forking workflows, because they are of higher value to our users. We're not ideologically opposed to them (indeed, forks are useful for some professional workflows too - such as working with contractors or external contributors), but they just haven't bubbled up to the top of our roadmap just yet.
