Why do skiers often wear sunglasses while they are skiing

They do it for personal protection, while they are skiing rocks can fly though and without personal protection the can get injured or even killed. That why they wear glasses for personal protection to avoid being injured in the eye.

For example if you are cooking and you want to take something of the oven, you would likely wear some hand gloves to avoid burns, that's the same with skiers.

There is a lot of glare off of the ice, due to the sun and it also is always good to have eye protection in case you fall face first : P