Three days passed since the Ares Incident.
The UA Secretary of State paid a diplomatic visit to Xin and met with Celestial Trade's Space Head, Kelvin… In fact, they originally wished to meet Jiang Chen, but Jiang Chen refused on the basis that he was on vacation.
Vacation.
It was a good excuse.
In short, Kelvin assumed Jiang Chen's role and euphemistically expressed the difficulty of the rescue to the visiting UA Secretary of State. For example, Ares landed directly above the Devil Worm's nest. If the rescue may cause the astronauts on Ares to be killed or injured, Celestial Trade would be unable to take the responsibility.
In short, we can't save your people!
While the Capitol was furious with Celestial Trade's stance, there was no other solution.
After all, no agreement was in place between the two countries. Offering assistance would solely be on the grounds of humanitarianism.