In this era, in my opinion it is steel shot and the lack of ammunition selection.
If you look at the 12 and 20 gauge, there are lots of choices in type of ammunition and shot sizes. Go into Bass Pro or Gander Mountain or any other "big box" store and you will find 16 gauge, but often it is either good quality #6 or 8, or economy grade. Very few even carry steel in 16 gauge.
The lack of readily available non-steel choices of non-toxic shot also hurts it. Sure you can get Bismuth, but it is a mail order proposition for the most part.
I don't think it is dead, as many have proclaimed over the years. New shooters discover it every day. It is my personal favorite. Browning keeps it alive here in the USA, and RST keeps us stocked with quality ammunition for vintage guns.
I would like to see Remington re-introduce the classic, "Shur-Shot" load in 16 gauge. Most of the loads I find in the stores are high-brass or Federal Magnum loads, which really are not needed for the gauge.
