Ive heard the 16ga died thanks to the shotgun manufactures themselves. The story goes that because it was such a perfect balance between a 12 and 20 that they would only sell one gun that could do everything instead of 2. They wouldnt make many popular models in 16ga to force people into buying a 12 for certain things and a 20 for others. IDK how true it is but it makes sense.I feel the same way about 16 gauge shot guns & shells.
Why has this gauge died out? It used to be very popular -- splitting the difference between a 12 and a 20 gauge.