I believe it's also the case that ALL Television advertising (and most ads in general) are incredibly overvalued. Most Marketers already know they're blowing 50% of the budget, they just don't know where the waste is (hint: everywhere). Most large corporations run on high enough profit margins that they can do this, and people are happy constantly spending all of their extra income on consumer goods. I wonder what the future holds...
Part of it was driven by growth in cable revenue. Customers are paying nearly 30 dollars a month that gets passed to cable stations.
I think another part of it was the assumption that netlix and Amazon will payout to get a license to your content later.
But really I think it's the collapse of the broadcast networks. It used to be everyone just watched whatever the big four had on. So now the wealth is being spread.