If you are going to play tennis (or do anything for that matter), you may as well look and feel good while you're doing it.
Come to think of it, that goes for just about any activity. Even if you don't feel good, you have an advantage in knowing that you at least look like you feel good.
I love when I'm able to find the perfect cross between form and function. Looks good on and does the job. For me, this outfit nails it, even when I don't play my best. So why wouldn't I wear this, even if everyone else is in t-shirts and shorts? I can't think of a reason.