There are a few reasons I prefer natural materials for my clothes.
1: There are studies that show reports of carcinogens in synthetic materials.
2: Natural materials breathe much better than synthetics. You will sweat less and smell better in naturals. Try wearing synthetic socks if you don't believe me (I don't actually recommend this... It's gross)
3: A well made and maintained piece of clothing will last a very long time. That being said, there are not many well made...