The PRC actually refused international aid. Mao was… not the sweetest fellow in the candy shop.
In addition to the historic reasons mentioned in the other comments, there’s places facing famine right now that aren’t getting much help and several more countries where we should be preparing for mobilization and aren’t.
Source for that image is the World Food Program’s early warning report: https://docs.wfp.org/api/documents/WFP-0000153539/download/
Because the Chinese government (Mao) refused to acknowledge that it was happening. He surrounded himself with yes men so probably did not even know himself until it was too late.
He also ordered many from the fields to factories and mines. Reducing the number of people farming in a misguided effort to industrialize imitating Stalin. Ordered sparrows to be killed because they stole grain. Leading to a boom in the locust population causing a plague. Heard somewhere that soil volume was important to food production. And being the supreme leader and less then a novice in the subject matter. Ordered those that remain farming against their objections under penalty of death. To till glass and other junk into their fields to increase the volume of the soil. Making the soil useless and infertile for a long time.
This is why all centralized authoritarian style governments are deadly. Whether it’s Hitler Stalin Lenin or Mao. Theoretically if we had a wise and benevolent leader. It would be the most effective and beneficial form of government you can have. The problem is with wise and benevolent leaders. It’s often more perception than reality. And simply an outcome of the environment they find themselves in. And even then they still tended to be the exception and not the rule.