They specify frozen food. No mention of fresh food although it's a possibility, I suppose. I wonder if the state of being frozen helps maintain the stability of certain biochemical agents.
Good question. I'm guessing a few things. Frozen food probably stays around longer on the store shelves and isn't inspected the way fresh food (I.E. meat) is inspected. But this is a very weak theory. It all depends on where the point of insertion is I guess.