https://foreignpolicy.com/2019/03/21...s%20Picks%20OC

So important is the China-Pakistan partnership that Beijing was willing to stick its neck out in support of a key terrorist asset of the Pakistani state who garners little sympathy outside Pakistan.
While most understand that China and Pakistan have a close relationship, many regional experts thought China had the upperhand in the relationship, and had the leverage to support the UN effort to designate Azhar a terrorist, but instead China placed a technical hold on the resolution.

Perhaps the biggest reason to have believed China would let Azhar be designated a terrorist is that it would have been a low-risk move for Beijing. Pakistan’s close friendship with and deep dependence on China—which increased after the United States suspended its security assistance to Pakistan last year—means Islamabad would have been in no position to express displeasure, much less retaliate. So there would have been no deleterious consequences for bilateral relations. In fact, allowing the resolution to pass would have benefited Beijing: It would have brought China some international goodwill at a moment when its global image has been marred by its cruel and repressive policies toward the Uighur community.