I think it's more perception than anything. You're also stuck with black as a one of the components of the colorway, which may limit what looks nice aesthetically.
There are also engineering limitations for composites since they usually have to be beefier in certain spots to survive.
However, the firearm industry has been transitioning to composites for a while now. I think you'll see that more in paintball on mid ends, transitioning to the higher end lines (ie Etek5)