What's more likely is these were cars were boats built on ancient body-on-frame platforms into 1990's, which were killed in sales by Japanese sedans perceived as more efficient reliable (Honda Civic, Accord or Toyota Camry/Corolla). Not to mention the body-on-frame sedans were not up to increasingly stringent crash tests, which required crumple zones. The B-Body platform Impala you refer to is a variant of a platform that was introduced in the 1920s!
Look at how much US market share GM bled in the 80s going into the 90s. The products were not competitive.
The big three American manufacturers were viewed as unable to compete in the sedan space which is why they pivoted to the truck and SUV market, which continues through today (not coincidentally trucks and SUV benefit from CAFE standard loopholes along with the protectionist chicken tax, a 25% import tax on light trucks [0])