Because actions have consequences, and unlike the Americans, China plans ahead to ensure the consequences align with their strategy and time frames, rather than do knee-jerk reactions for one second of gratification at the cost of longer term pain and damage.
Japan is not a peripheral power, and to do serious economic damage to them will also cause countries all over the world real and serious pain and damage. This is why China is going out of its way to appear to be the reasonable one. Because it doesn’t want to needlessly alienate peoples and countries when the economic pain starts to hit.
The Japanese comments are an unprecedented provocation, but they are still too minor to justify significant economic retaliation by China.
China wants to dial the pressure up slowly by manoeuvring Japan into making mistakes and sounding belligerent and unreasonable to justify Chinese retaliation. And it’s working. Every time China complains and apply a little more subtle pressure, the Japanese doubles down and make another offending remark or escalation.
By the time Europe and the global south starts to feel the spillover economic pain themselves, they would have already been conditions to pin the blame squarely on Japan instead of China.
That means no solidarity and outside support for Japan. Making it much easier for China to isolate and de-industrialise it.