Meg, I'd guess that participation in whitewater plays the biggest part. The 90's and eraly 2000's were the heyday of whitewater when there was a big buzz around paddling and a lot more companies pouring money our of their marketing budgets to sponsor events. Now there are only a handful of manufacturers and they are all just trying to squeak out a sliver of the market share.
If whitewater had the same numbers as golf, mountain biking, or skiing, it would be a different story.