Did you ever tried to punch a dragon to death?
Seriously, who would be suicidal enough (in-game) to go engage a dragon in unarmed combat? My guess is that, assuming you tried, you died a lot of times until you realized that you'd be better off with a weapon or a arsenal of spells.
Anyway, is there any more ways in which, outside of a beast form (werewolf or vampire lord), unarmed combat is a complete and utter liability?
Also, kudos to those who DID killed a dragon with their bare hands. Now, go grab a weapon and better your chances of survival.