I'm not dismissing malice or opportunism in the media, but it is also important to appreciate the situation mass news media is in. Mass media are extremely dependent on things like advertising and that's always been the case for as long mass media have existed. The price of subscription or buying a paper is simply too meager to cover the costs of running a paper, for example. Advertising introduces its own perverse incentives and limitations (you can't bite the hand that feeds you, for example).
24 hour news are, for the most part, useless, so they've got to fill the air time with sensationalized garbage, and because there's an arms race, the sensantionalism escalates.