People think black looks cool just like in the 80's, and black is even more of a status symbol now because carbon fiber is black. Aluminum can be painted or anodized black more easily than carbon can be painted tacky silver, and due to the prestige of carbon, it's aluminum that wants to imitate carbon, not the other way around. There's also an increasing number of plastic parts, so those end up black by default just like a Simplex Prestige unless they're painted silver, which happens sometimes with Shimano.