Why don't aircraft (commercial and military) use reflective visor windshields?
Reflective materials cut down the amount of light let into the cockpit, which is useful in very bright sunlight, but would be undesirable at night. At night these materials could potentially blind the pilot, so you would have to make these materials retractable somehow, which would add complexity and weight. Over time these coating would be damaged by airborne debris, smashed bugs, and regular wear and tear. Add this that these coatings are expensive - outfitting them would be a significant cost. 

Add to this that ever pilot would have different tinting needs - some people with less sensitive eyesight would need less tinting and others more. It's far cheaper and more effective for people to simply buy sunglasses.