Why are standard eyeglasses or everyday sunglasses an insufficient sole substitute for a proper helmet visor or goggles?

1. Eyeglasses are too dark for bright desert sunlight
2. They do not seal around the eyes to prevent wind, dust, insects, and road stones from causing sudden blindness
3. Eyeglasses are illegal to wear while operating a motorcycle in Bahrain
4. They cause the helmet chin strap to loosen automatically