Why didn't Japan call for the ICJ to settle the dispute over the Senkaku/Diaoyu Islands? I am asking this question, because Japan took it's ongoing dispute with South Korea over the Dokdo islands to the ICJ, so I am wondering why Japan didn't do it in this particular case. Wouldn't a call for arbitration put China on the defensive in the same way it has put Korea over the Dokdo island matter?
China is unlikely to listen to an ICJ ruling, so it carries risk for Japan if China wins and no gain if Japan wins.
From the Spratleys, where the Phillipines brought the case, to the ICJ (aka Hague Tribunal) in 2016, and won against China:
Beijing has criticised an international court’s stinging rejection of its territorial claims in the South China Sea, with Communist party-controlled newspapers warning of a military escalation in response to what they denounced as a US ploy to thwart China’s rise.
Regarding the details of this case, see Philippines v. China @ wikipedia.
Just look at the situation in the Spratleys 5 years later. China has doubled down instead.
On the other hand, South Korea is more likely to act in good faith.
Note that this is not something Japan would cite as a reason, as it shows weakness.
Edit: please see comments by xngtng below, who raises some valid points re. this answer.
This article in the Center for Strategic and International Studies appear to answer your questions:
Japan’s position on the Senkaku Islands is clear. Japan took measures to incorporate the islands in January 1895 after having carefully surveyed and determined that the islands had been terra nullius (no man’s land). Ever since, the Senkaku Islands have been under the Japanese administration except for 27 years between 1945 and 1972 when the islands as part of Okinawa were under the US administration but returned to Japan along with Okinawa in 1972. Thus, the islands have been under the effective and peaceful administration of Japan for more than a century. It is clear that the Senkaku Islands are an inherent part of Japan, as evidenced by both historical facts and international law, and therefore there is no “dispute” about the sovereign title of the islands.
What the article's author thinks China should do
China’s Desired Action
If China considers that their assertion is really good enough to beat Japan, what China should do is to bring the matter to the ICJ. Since Japan does not consider the Senkaku issue a “dispute” there is no reason for Japan to sit and negotiate with China over the sovereignty of the islands. It is the Chinese side that should take the initiative to transform the issue into a legal dispute, because it is China who is seeking to change the status quo long established under international law.
How could China make it a legal dispute? It is actually quite simple. All it has to do is refer the case to ICJ, just like Japan has been trying to do with South Korea over the Takeshima Islands dispute. If China decided to take this course, Japan would not run away from settling the issue at the ICJ.
The author suggests that China is the weaker party and therefore should take the matter to the ICJ - not Japan, who is the stronger party and currently exercises control. Unlike the Dokdo/Takeshima dispute wherein South Korea is the stronger party and Japan the weaker one.
Disclaimer: the article's author is a Japanese law professor at a Japanese law school, which might slightly bias his opinion in Japan's favor.