Nobody ever said China couldn't run DDOS tools. This is a deterrent signal sent to businesses outside of China. It publicly demonstrates that China has the will to punish businesses for serving certain kinds of content. Although it's obvious who benefits, it's just deniable enough that they have avoided international censure; today nobody can reasonably think "China wouldn't do that because they fear reprisals," since they just did it; which helps China maintain a credible threat to businesses. They aren't trying to destroy GitHub, just to exert control over businesses which are out of their regulatory reach.