Should anyone care? Once someone launches a DDoS, their argument is invalid. And reporting the grievance might just encourage them.
I don't know anything about any of Github's attackers, but from other incidents I know of at other services, it could be anything. A billing dispute. Anger that something was taken down... or not taken down in response to an unreasonable request. Anger that an account was suspended... or that some feud-rival's account wasn't suspended. People throwing "do it my way or I'll take your site down" tantrums may not make sense to anyone other them themselves.
