This is due to the fact that upper body muscles have more androgen receptors than other muscles and respond better to resistance training. This is why new steroid users see their shoulder, traps and back explode very fast in the first few steroid cycles. Of course, leg and torso muscles grow as well but never as fast. This is what causes the ”V-shape” in roid users who normally wouldn’t have the genetics to produce a wide shoulder/thin waist body.