15: Chevrolet Vega
The Vega was not a bad concept initially. Take the fun to drive the formula of the Camaro and shrink it down into a gas-efficient package. Aesthetically, the Vega looked like the Camaro in many aspects, and consumers went for the attractive package. The Vega was panned for a lack of reliability and cheap build quality, with many defects coming straight out of the factory (via Macs Motor).
Compact cars coming out domestically around this period were not promising at all. There was a lot of potential with the Vega, especially considering the mini-Camaro styling, but it wasn’t enough to propel the car to success. When GM discontinued the Vega, it had not made a significant enough dent in the market and the competition was still for these compact cars at the time.