one lapse in judgement
As TotD says, it wasn't one lapse. There are plenty of examples of lapses in judgement - overflying maintenance, ignoring a Bingo fuel, busting an assigned level. These are all serious enough, but unlikely to kill you instantly.
This guy on the other hand ignored repeated stall warnings, failed to ever achieve the correct speed for the aircraft configuration, failed to establish his assigned minimum height, and when the laws of physics invariably took over, he failed in a fundamental way to recognise, correct and recover from the stall - that most basic but critical of flight manoeuvres.
As for CRM, the co-pilot learned that the price for reacting to a "Flaps" call without ensuring the correct flying speed was attained, was the same as the price the safety observer paid for failing to ensure the sortie was flown within the aircraft and authorization limits - and that was the real tragedy.