As with all medical advice, they take the majority over the minority in everything, so if a normal healthy person can eat every type of food and its healthy for a normal healthy person, so why can't everybody, because it's healthy!
Anyone with a food intolerance (including all types of diabetics) food allergies, or thyroid issues, hormone imbalances and so on, there will be a reaction to that food, wether it's relatively small or something as serious as a peanut allergy which could be fatal!
There has been many studies done on people who have allergies, and always told to avoid the food they are allergic to!
Why isn't it the same for people who have diabetes?
If a certain type of food makes you ill, they why are we told to not avoid it but eat smaller amounts of it! (Go figure!)
There are always alternatives to all types of foods!