The lines themselves aren’t that different on most of the cars that were “Retro Rips” like the Challenger and previous generation Mustang. The Charger - that doesn’t count because the product just happened to get the Charger moniker but has nothing to do with the original 2 door coupe which bore it’s name.
The Camaro was more aggressive and futuristic. But the overall trend you notice applies to almost all cars, not just muscle cars.
Big wheels drove higher belt lines. Higher beltlines drove smaller green houses. Pedestrian impact guidelines drove bigger front ends.
We forget as designers that so much of what goes into those designs has as much to do with skirting around all these health and safety guidelines as it does with styles that resonate with people.