U.S. would not want China to follow its behavior in refusing to abide by international law
Of course, China’s withdrawal from the convention would weaken the reputation and authority of the tribunal and international law in general. It would also give notice that China is not to be trifled with — that it will not “be taken advantage” of by small Asian countries — some still influenced by their former colonial masters.
Unfortunately there is a long political history of world powers using, not complying with, or making new international law to further and protect their interests. Prime among these has been the U.S. Its refusal to join the 1982 Law of the Sea Treaty and the International Criminal Court, its withdrawal from the ICJ case, and its “invasions,” cyber and drone attacks, and interference in the internal affairs of other countries have certainly set a bad precedent.
The U.S. and its Asian allies need to be careful lest they push China into actually being what they fear most — a rogue country that uses might rather than right in its international relations.
Let us hope that China considers the costs of withdrawing from the treaty greater than the benefits.