are Chinese very skimpy about aid to North Korea? or why so much run-around with Western food aid?

AFAIK the sum total of food aid to North Korea is on the order of a million tons of rice per year, and often a lot less than that. A ton of rice now sells for on the order of $500, maybe in the past it was closer to $800. Well, so the amount of money involved seems somehow trivial, on a national scale. So why don’t the Chinese just increase the aid budget slightly, provide all the rice and let DPRK posture against America without bothering about the food aid? Or maybe force North Korea into allowing more productive Chinese investment that would have generated equivalent export earnings?

Is China being very stingy? Do they just like to humiliate North Koreans? Are they trying to deceive Washington and Seoul into thinking that all this food aid is such a big deal and capable of restricting North Korean actions whereas presumably Beijing could tomorrow just replace it with a stroke of a pen?