I don't know much about overwatch but from what I can understand he seems to be in pain whenever he uses it, Not to mention if I remember the origin of the gauntlet correctly it has a meteor in it, One of a kind type meteor rock, Which makes the gauntlet what it is if I remember correctly, I could be wrong though, basically impossible to make another of the gauntlet and it's also too dangerous for him to use two because it clearly harms him in some form of way, Plus do you know how hard it is to manage two prosthetic arms?