The reasons for this situation range from poor engineering and agricultural practices, inadequate transport and storage infrastructure through to supermarkets demanding cosmetically perfect foodstuffs and encouraging consumers to overbuy.
I know it's important to know and it's major news, but it just really bums me out and really gets to me. My mother was telling me that we used to have a vegetable truck that would deliver vegetables to our estate. The owner one day said he had no mushrooms, only old ones, and told him that they were fine and were perfect for mushroom soup or sauce. He had just been throwing the old ones away the whole time. I think if people had better knowledge of how to use what they have and the point where something isn't edible anymore (rather than the really safe supermarket suggested dates), we could save so much.