That clone is made to resemble the SS, a copy of the popular hi performance trim line, it was probably just a Chevelle, then the Bucket seats and console added and engine add ons or a switch. The VIN will show that it is not an SS but it can be just as powerful
Because it isn't a real Chevelle SS.
Its not original, its a copy and holds less value than the original..
When they call a car like this a clone they mean that it started life as an ordinary Chevelle (for example) and then in recent history has been restored and re-engineered to look like, behave like and altogether be for all intents and purposes an SS. This is common practice where things like so called hot or rare and desirable versions of quite mundane family cars exist.