If wounds develop (due to increased pressure or injury) then increased blood sugars will feed any infection present making the wound worse. The longer you have a wound the greater the chance of infection. Or even a small fungal infection may enter your skin and become a rapidly spreading soft tissue infection or sepsis.
Excessive blood sugars contribute to reduced blood flow (high cholesterol, high blood pressure, sedentary lifestyle). Basically, not enough blood flow means a wound cannot be supplied with the nutrients and oxygen it needs. This is called Peripheral Arterial Disease (PAD). Patients suffering from PAD have a high chance of developing gangrene (tissue death).
Treating small wounds or sores quickly reduces your chances of developing an infection. It is not that getting a wound means it won’t heal, it just takes longer to heal. Long-term uncontrolled diabetes may need surgical intervention to improve circulation, remove infected tissue or amputate areas of tissue death.