I cooked and gave out cheeseburgers at a soup kitchen tonight... had a few of the leftovers myself, as it was that or throw them out. (they have unusual rules... why not give it away? they have limits... strange)
now, it's honey roasted peanuts.
Having been on both sides of the issue in countless shelters and soup kitchens (as a recipient of the food when I was on the streets and later serving the food as a volunteer), I can take a guess:
It might seem unfair, but you have to set that limit because if you don't, then you'll just keep giving away the food until it runs out. When that happens, some people invariably received a third helping while some didn't. This makes those who didn't jealous and can lead to bickering and all-out brawls (I've seen it.)
Hunger and poverty aren't very conducive to rationality. It tends to put you in a survivalist mindset, and when you see someone in your same situation being treated better than you, it can lead to hurt feelings and temper flares.