What truly killed off the 16 was manufacturing consolidation. Starting in the 60s the trend was to use a 12 ga frame for the 16 which gave the 16 no advantage. If one is going to carry 12 ga weight, they may as well carry a 12 ga. Light weight 12 ga guns as well as the hype of the 3" 20 ga did no good but it was the weight issue which sealed the 16's fate.
Then a brief resurgence in the 16 ga occurred in the late 80s and some were built on the 20 ga frame. They carried well and made good upland guns. 20 years later (see kind of a trend?) the 16 popped up again but the result will be short lived. The requirement of non-toxic shot will be the death knell of the 16 as it is not large enough to make good use of steel shot and it is in too little demand to garner the development of affordable non-toxic shot of other types. Even the 20 ga will suffer greatly as it too will have difficulties with affordable non-toxic shot.
