The issue with forking is that you take on a lot more responsibility than you did by submitting a PR.
Many of the people submitting PRs probably already contribute to projects that depend on Cairo. They may even maintain those projects. They may not have spare bandwidth to take on the maintenance of Cairo too.
Many of the people submitting PRs probably already contribute to projects that depend on Cairo. They may even maintain those projects. They may not have spare bandwidth to take on the maintenance of Cairo too.