In the case of lightweight armor the movement is not reduced too much by the weight, but with heavier armor like plate or scales, the movement speed is impeded thusly that people are breaking the aesthetics of the full set by not wearing gauntlets and boots, with the intention of regaining more movement speed in pvp.
I think maybe its a good idea if you get a small bonus when you put the full armor on. For example +5% / + 10% armor (damage absorption) or something similar to encourage people to wear full armour set.