Two things: The rising cost of making television and enough cord-cutters abandoning the cable bundle to blow up the business model. The first trend is happening. The second one isn't.
If I could quote the whole article I would. Suffice it to say cable will eventually reach some sort of breaking point between rising programming costs and stagnant middle-America wages. Eventually enough people will deem $100/month for TV as a waste and will start dropping the telcos or they'll cut the TV cord and just opt for Internet access for content. If either of those happen then ESPN/CBS/FOX can't demand as high of a price because there's no eyeballs to sell to advertisers. The question is which one comes first en masse. For either to work it has to be a serious number of people (10's of millions). It's all about the eyeballs!
As Derek says,
If you're interested in the future of TV, don't pay too much attention to the remotes and the guides. Just follow the eyeballs. They're still tuned in.