There is a big difference between support, and noise. There is a lot of NOISE about the 16 ga., but look around any gun shop for a 16 ***** shotgun. You will be lucky to find 5% of the guns in 16ga. There is nothing wrong with them, but the same reasons for it's demise are true today, as in the '60's. The recent NOISE, is just a bump in the chart. The same applies to ammunition.
Just imagine you are a manufacturer. Try to justify investing millions of dollars to tool up for the 16 ga. your board will have your head!