I think car makers just sell what people want. If you go back to the 80's, when today's form factor first evolved, the American cars were still pretty distinctive. I clearly remember the Chevy Caprice type cars (and all the variants from Oldsmobile and Pontiac), the Ford sedans, and Chrysler cars. You still had station wagons galore, big bumpers. You know what the top selling car was at the end of the 80's? The Ford Taurus. Front wheel drive, unibody, bleh. Fast forward a few years, all the car makers were making front wheel drive unibody. No style at all. There were still a few models sprinkled in here and there, like the Thunderbird, but slowly cars drifted toward the unibody, and bleh.
Now it's just CUV's and SUV's and more bleh.