Honest question: why would China care if Baidu is null-routed by the rest of the world?

1. They lose the ability to use it as part of a similar attack in the future. They can't use the same trick too many times or it stops working, forcing them to work their way down a list of pawns.

2. It damages their relationship with Baidu and indirectly with other Chinese tech companies, in much the same way that NSA overreach affects US ones. There will be some internal political effects, depending on what stakeholders have political clout.

3. When external Chinese-speakers use Baidu, the government has some influence on what they do (or don't) see. If they are forced to other alternatives, the government loses a certain degree of information-control.

Because once it's nullrouted, it can no longer be used as a weapon. They only have so many cannons.

The GitHub attack apparently targeted sites using Baidu analytics visited from outside China, so outside visitors are weaponisable too.

They are, as long as their ISPs don't block Baidu.

perhaps targeting ads to the large Chinese diaspora provides an effective way of redirecting some of the wealth accumulated abroad back into China.