Why are some patients of diabetes treated by giving injections

Why are some patients of diabetes treated by giving injections of insulin ?
A. 1) Diabetes is a condition in which sugar level in blood is very high.
2) Insulin hormone is released by pancreas glands which regulate the blood sugar level.
3) In diabetic patients pancreas is stopped releasing insulin hormone.
4) If it is not secreted in proper amounts, the sugar level in the blood rises, causing many harmful effects.
5) Due to this reason diabetic patients are treated by giving injections of insulin.