My guess is if the motivation is political, then China wants to send the message that the ISU needs China, not the other way around. With such a short notice and since GP's probably aren't terribly profitable, China may be banking on the ISU having difficulty striking a deal with the Korean federation (and other prospective hosts) to take on the replacement events. The point of a protest is to inconvenience and disrupt, after all. If the ISU must go through a massive headache to work out event logistics and/or make major concessions to other federations in order to get them to agree to host events, they may become more receptive to quickly resolving whatever conflict they have with the Chinese federation.
Personal conspiracy theory: China is hoping for a situation where it turns out no one wanted to host the GP (or whatever important speed-skating events were planned). Then, the ISU finds itself in a difficult situation and acquiesces to Chinese demands, and, all of a sudden, China discovers an arena which isn't being renovated and announces the Cup of China is back on. Don't forget to say 谢谢, ISU!