We tend to overlook the effect of the packing house.
It has been proven that citrus taste far superior before they enter the packing house, than when they exit.
All that bumping around, whilst washing, waxing and heating effect the flavour. Not to mention the time spent off the tree before it reaches you at the store.
Perhaps GN is one of those varieties that doesn't hold up to the rigors of modern handling as well as other varieties.