These stat numbers for BOTH CNN and FOX tell one simple story... CABLE TELEVISION is going the way of the vinyl record album.
Who needs Television? "NOT I", said the little grey hen.
Both CNN and Fox are accessible through Cable and through streaming services. Just as recording artists transitioned from vinyl to CD to other media - "Cable" news networks are being accessed outside of cable.
Are the majority of Americans ditching legacy news networks? I don't know. What's true is that there are many, many more news outlets today compared to the 60s, 70s, 80s and there are also more vehicles (TV, Smartphone, PCs ...) for receiving news than any time in history.
Bottom line: We have more choices today for the type(s) of news we receive and how we receive that news.