Oh my God, I'm so amazing!

Not actually true, at least it wasn't last time I checked, you are allowed to use gears if you are in a purely indivdual event, pretty much the only event where you can do this is the kilo (or 500m for women).

It's not often used, probably because most think that it's not worth the effort with mechanical problems, extra weight etc, you may as well just get good at starting.

"1.3.025 Freewheels, multiple gears and brakes are not permitted for use on the track during competition or training. Disc brakes are forbidden in cyclo-cross training and competition."

http://www.britishcycling.org.uk/nmsruntime/saveasdialog.asp?lID=459&sID=122