as the old saying goes, all the holes in the swiss cheese lined up and an accident happened.
Contrary to common misconception, if there is one thing that mishap investigations have proven, mishaps do not just "happen". A mishap is caused. The swiss cheese does not randomly line itself up, the slices are selected and put in place with a given edge facing up. The job of the mishap investigator is to identify "causal factors" so that the next aircrew can learn from this and not put a stack of swiss cheese slices together in the same manner. A technical mishap investigation (which is what the NTSB does) is not looking to affix "blame" on any particular individual, but to identify the factors (to include individual and crew behaviors, qualifications, equipment function etc) that contributed to causing the mishap. If the mishap is the result of a given crew member not flying the aircraft properly, then the question is why, for if the why is not known, future occurrences cannot be avoided.
Eliminate undesirable causal factors, and you eliminate deleterious results.