Water skiing is hard - it’s work, so is snow skiing and even worse snow boarding. Tubbing is easy. Computers and video games even easier.
Millennials, Gen X,Y, & Z‘ers. Are not gonna do it. You could give them a free boat, skis and a lake house- still not gonna happen. I have a bunch of rental properties so I see how they live and think. Argue this all you want but I bet the decline is pervasive across all sports