Why are diabetics being told to eat what made them diabetic?

Thursday November 14th was World Diabetes Day.
Definition
The International Diabetes Federation (IDF) defines diabetes as follows:
"Diabetes mellitus, or simply diabetes, is a chronic disease that occurs when the pancreas is no longer able to make insulin, or when the body cannot make good use of the insulin it produces. Insulin is a hormone made by the pancreas, that acts like a key to let glucos...