it's a simplicity and way of riding thing. On the tracks, you don't need more than one gear because it's flat(banked on corners) so more gears won't do anything for you. Track bikes are also great tools for training to ride geared bikes. You learn to spin better, and you learn what your best cadence is. It's a lot of different things. I used to wonder the same thing until I tried it and it becomes clear once you start to ride fixed. I'm sure others will explain it better since i'm still a relative newb.