It must be the automatic tranny. Alot of people don't want to deal with a stick shift, never mind a 6 speed.
I see 98% of Camaro Z28's with automatic tranny. I would never get that considering the fact that Chevy will give you the same exact 6 speed that is in the SS's. I could see if they had a 5 speed stock and people didn't want to pay for the 6 speed but come on people, it's a sports car. Drive it like one.
You know, I bet for the hell of it, if the automatic was the standard option and the 6 speed was an 1500.00 option as was called the "super lighting transmission" people would buy it more. I don't know, if you ask me, it doesn't seem the SS stand's for anything these days, look back in the 70's the Z28's and SS's were two complete different animals. Once was made for the strip and the other was made for a road with turns. Different motors were options, different suspensions, different weights and all kinds of stuff like that. Times change I guess.