In previous threads about Github being DDoS'd, I asked the same question.

Apparently it's some scheme to ask ransom from companies/startups that have enough money to pay and/or not enough infrastructure to sustain the attack without giving up.

Yep. There's a well-written article about an early DDoS extortion attempt where the victim fought instead of paying, developing some novel protection technology in the proces: http://www.csoonline.com/article/print/220336

Yea, all of us successful web companies face these all the time. We get them multiple times a day. Most of us end up giving up and pay for Arbor gear and ridiculously over provisioned pipes as well as good relations with our hosting facilities.

Additionally, some group may be targeting a specific project on Github