Thats why they don't wear sunglasses, don't wear a hat and use cool-looking 87 sq in rackets.
Imagine not able to see the beautiful eyes of Federer's on court and watch how his hair flows against his fingers. Tennis even life becomes so meaningless.
Sunglasses can be bothersome in tennis, they can fall off in a scramble and it can get in the way of your vision, even slightly. Some people can use it, it's much simpler to not.
Same with a hat, I dislike using hats, they don't stay on if you're in a mad dash and can be an annoyance during crucial moments when there are more important things that demand my attention.
Regarding the smaller head size, it's a matter of preference. Try them some time, it astounded me with how much feel a smaller head has. I used to be intimidated by the head size and never gave it a chance until I tried one for fun and immediately noticed a world of difference in feel that a bigger stringbed just cannot emulate.