I think your example of your kids' interests is exactly why that demographic is seen as so valuable for advertising. One poster has a middle-aged interest in

I think your example of your kids' interests is exactly why that demographic is seen as so valuable for advertising. One poster has a middle-aged interest in hard sci-fi; for $x advertising allocation per individual it's going to be difficult to shift his interests. The same $x applied to teenagers year after year 'flips' them from one revenue-generating interest to another. And sets them up, the advertisers hope, for a non-niche middle-aged interest.