- Raising awareness of self-hosted alternatives

- Getting people to use BB instead

- Fake DDOS to get more companies to pay for github:enterprise

- Preventing a system upgrade in a company which has deployment relying on github

There are lots of potential ways to use it...

My guess would be attention and publicity. Targeting a technical, developer centered site is likely to require more "skill" as one would expect such a site to have their defenses ready for this. All the greater challenge. Secondly, every time this happens it causes quite a discussion on developer forums and sites such as HN. If you're seeking attention and "recognition" amongst technical people, what better site to attack?

Maybe a developer killed their parents?

Probably to disrupt businesses that rely on github or cause a service to function improperly causing a security loophole they can exploit.

The goal may be to potentially open up a new attack vector to steal code, some of which may contain secrets. This is pure speculation, but a definite possibility.

Maybe they want to disrupt developers working for a big bad company.