You have small balls, that's why.

Let me explain. Testosterone is responsible for the development of all male characteristics, i.e. facial and body hair, muscle mass and also male genitals. If you can't grow a decent sideburn, that means you don't have enough testosterone, and thus, small balls.

Hehehe... I'm just messing with ya.

If you're chinese, then it's a racial trait. It's in your DNA not to have too much hair, so there's not much you can do there mate.