When sales of soda in the USA dipped in 2006, everyone assumed it was a blip. They'd been steadily increasing for twenty years; why would they suddenly start going the other way now? Then it happened again. And again the year after. And again the year after that. Now, it's a steep decline that nobody can see a way out of. Pepsi sales by volume are dropping by five percent each year. Coca Cola is doing slightly better, but they're still seeing consistent falls of two percent.
The whole time they were growing up, millennials were told that too much sugar rots their teeth, and that soda is bad for them. They listened to the advice their parents and dentists gave them - and now they're being blamed in the press for killing an industry. As millennials do appear to be more concerned with having perfect teeth than any generation in the past, this one isn't all that surprising.