It isn't of course. And one only has go back and read the history of the National Broadcasting Company (NBC)[1] where it was sued by other voices trying to break into a market dominated by a single media company.

Oddly enough it is exactly like Google in a way, the ability to sustain a network depends on the ability to sell advertising which depends on viewership for pricing. And being unable to get viewership denies an ability to exist through advertising. So having a monopoly on advertising makes you the defacto monopoly on the viewership because it denies capital to a competitor to develop additional viewership.

[1] https://en.wikipedia.org/wiki/NBC