For whatever reason one of the Swiss cheese slices (namely the crew) aligned its holes with the RA slice.
While we all agree that we have to strive to maintain the highest possible SA, we are still a slice with some holes that dynamically vary in size and position.
That's why over time we have added more and more slices, GPWS, EGPWS to name a few.
Sure we can fly without them, it's been done for ages, but they surely have improved aviation safety by saving some arses, maybe mine one day.
I wish Boeing had mounted a RA comparator on those NG's that had saved the day.