I feel like historically, within the game, the weapon has been the single most important representational item of the player. You could argue mark, but when things happen to the player, it is always to the weapon thus far.
This could change but I think that a weapon is something that is kind of wield while fighting while a shield is not less used but less controlled. In that sense you are freezing the opponents arm so they can't swing it. This would not matter so much on the shield...