Glasses - A Dearth of Choice

Despite being in need of a new pair I've been putting off buying glasses for the past 3 months. The reason is simple, despite there being a vast selection each of them are so very similar.

Why is the world of glasses - a medical device - so intertwined with fashion? It's at the moment it's almost impossible to buy a pair that isn't thick, black framed that dominate the face of the wearer.

How is a dearth of choice reduced to just a single style?