I'm not prone to violence but if I met someone who I was certain DDOS'd Github I'd certainly immediately punch them hard in the face.

Github is a noble company with noble end-goals, and collaborative open-source is a revolutionary "work" idea. To see someone smash a bottle on the counter and threaten the nicest guy in the room gives me rage.

Hard to specifically pinpoint, but clearly someone or a group of individuals that don't want to see GitHub succeed.

(black hat) hackers like to get people's attention, gain notoriety. Especially of their peers.

I'm gonna guess people are just assholes. It's quite the target, considering the number of companies that rely on them for their day to day operations. They can do a lot of disruption/damage with it.

Normally I'd say extorsion, but I don't see why the attackers would keep it up for so long.

maybe credibility, of all things. if they can prove they've been able to successfully ddos github, they can be expected to flood pretty much any target.