Though when you try out a new attack vector, the community (hopefully) publishes enough details about the attack to help the next target more effectively deal with that particular attack.
If someone is attacking whitehouse.gov or a similar target, I somewhat understand their reasons why (though I don't agree with them). github.com, on the other hand, while a for-profit corporation, is also a valuable bit of Internet infrastructure that makes the world a better place. Attacking targets like github.com, Wikipedia, and others helps no one, and forwards no coherent political agenda.
So I'm going with the "for kicks" / jerkwad theory.
Attacking Github means you deny many more than only Github as a target. Which I guess, makes it more valuable than another target.
I deal with this crap all the time.