[Agrajag]

If such beings existed, they would probably be too weak to use armor or weapons made from anything other than light wood or leather.
This is because as a creature grows in size (assuming his build remains the same), his strength/weight ratio decreases.
(This is because the strength of a muscle is determined by its cross section)

(With some reservations, of course. The way I put it isn't too accurate and doesn't really consider everything :P)