Paul at Curbside Classic, decided to sum up the demise of GM, and it was about the hubris and "Motor City Myopia"

 During the 1980s, GM had its greatest loss of market share ever, setting the stage for its ultimate demise.

https://www.curbsideclassic.com/curbside-classics-american/curbside-classic-1988-1991-buick-reatta-gms-deadly-sin-30-the-death-of-the-soul/