The real reason is that this bastard from Australia didn't play by the rules. While he was setting up FOX Network, he also acquired the Fox Film Corporation, which meant Murdoch was identified not only as a television mogul but also as a movie producer. Before the network even went live, Murdoch's Fox Film Corporation allied with other major film studios to lobby in the United States Congress and successfully pass a restrictive bill targeting television movies, which became the main point of contention that the three major networks despised.
Television movies are films produced by the networks for exclusive broadcast on their own channels, without a release in theatres. The primary reasons for producing these are to save on costs, as networks sought to avoid the hefty price of purchasing films from movie studios, which often involved package deals.