John Delorean gets much of the blame or credit.
He was appointed General manager of Chevrolet in 1969 to sort out their problems.
He wrote in one of his books that Chevrolet produced too many Engine variations.
His first orders of business was to de proliferate (eliminate) as many Engines as possible.
Corvette fought to retain the 454 LS7 but it also got chopped at the last minute.
1970 Corvette owners manuals even listed the LS-7 as an available Engine.
Fortunately, the 1970 Chevelle was able to retain the brilliant 450 H.P. LS-6.
Agreed, the 1970 LT-1 was a fine Engine but take up would have been too low.
At least the 1970 Corvette and Camaro got them before they were de-tuned.
Dick Keinath, of MK-II-MK-IV fame wrote all engineering effort went into emission work.
The High Performance era was over for a long time.