Earlier quoted context omitted.
From what I understand it's more of a delivery or logistics problem and its variations. Sometimes it's not worth it to certain people to deliver the food and in some cases someone takes the food before it arrives.
These days it's mostly an economic thing. Food's there but some people don't have money to buy it. http://www.worldhunger.org/2015-world-hunger-and-poverty-fac...
Also, it's kind of a good thing for economic causes to be producing excess. The other option is to be under-producing (because 100% efficiency is a pretty hard target to hit, you're either going to be over or under). If this was the case, it would drive food prices up. So even though there would be no waste, there would be even more want.