I think John Delorean had something to do with it, He went from Pontiac to Chevy on 2-15-69
There are books and Movies about him
found this on Wiki
"The executive offices of General Motors headquarters continued to clash with DeLorean's nonconformity. When he was appointed, Chevrolet was having financial and organizational troubles, and GM president Ed Cole needed a manager in that position to sort things out. The new model Camaro was due out for the 1970 model year, and it was rapidly falling behind schedule. Redesigns for the Corvette and Nova were also delayed, and unit sales had still not recovered from the past four years of turmoil, much of that because of the bad publicity surrounding the Corvair and well-publicized quality-control issues affecting other Chevy models, including defective motor mounts that led to an unprecedented recall of 6.7 million Chevrolets built between 1965 and 1969. DeLorean responded to the production problems by delaying the release of the Camaro, and simplifying the modifications to the Corvette and Nova. He used the extra time to streamline Chevrolet's production overhead and reduce assembly costs. By 1971, Chevrolet was experiencing record sales in excess of 3 million vehicles, and his division alone was nearly matching that of the entire Ford Motor Company."