The mechanism of forking and the GPL ensures tit for tat (you know, the idea behind capitalism). You can fork a project, but any improvements you make can be incorporated in the original code. So you get the benefits of forking (reviving projects), but not the drawbacks (leeching code). By assigning copyright, this mechanism is bypassed, and now they spent tat, but didn't get tit, so to speak. As I said, copyright assignment is something that happens in many many free software projects, and it's not morally intended to bypass the GPL, even though it does provide a loophole.
No announcement yet.
Nexuiz Gets Forked, Turned Into Xonotic