Looking at the graph in the article, ad spending on TV is at an all time high, it has just plateaued. So maybe revenue isn't the issue, maybe quality is.
It my guess that the TV networks somehow believed that if you made X amount of dollars on one channel, then adding a second channel would make you twice that amount. Networks that had one or two stations 15 years ago, now have 8 or 10. Rather than increasing profit, they are left with roughly the same amount of revenue, but they have to spend it on content for many more channels. Not wanting to close channels, networks started to produce cheaper programs, "reality" TV mostly. Meanwhile you can't buy a good, independent news channel, even if you're willing to pay.
TV can blame streaming, Youtube, the internet in general, but that's not what's "killing" TV. I believe it's the quality of the content that's the issue for TV.