The GTO failed because it showed up during the fuel crisis. Nobody is going to feel like buying a V8 coupe in a time like that. I remember driving past a lot of 6.0's saying "Where were you 5 years ago?"
I actually knew a couple people in the market for a car like the G8 and pointed them in that direction. It was like trying to sell a seat on the Titanic as the stern is slipping beneath the waves.
Apparently "bad timing" is not an acceptable reason for a car to not sell. (shrugs)