The shift happened around the same time that CNN and subsequent 24 hour news channels popped up.
A 1 hour news program can rely on it’s habit forming regularity and brevity to be a profitable vehicle. Morning news, evening news. These occupy limited time slots. Which enables the TV channels to effectively sell ads which support the program.
A 24 hour news channel will have a harder time pinning viewers down. It will also have a harder time covering all 24 hours of it’s schedule with profitable ads which 1 to 1 pay for airtime, overhead and employees.
The solution of course is to shift from news coverage, to entertainment. On Fox they are pretty blatant about this. They have regular shows with Oreilly, Hannity and other cranky old white guys. Viewers have formed habits around these shows and tune in, allowing ads to be sold.
MSNBC of course has Maddow and others with their own timeslots.
CNN, the oldest of them all has it’s own Anderson Cooper of course. But it also engages in a silly tactic of constantly flashing banners of ‘breaking news’ to make the ‘reporting’ seem more urgent. And changing the channel seem like a mistake.
What they all do is provide news based entertainment in between advertisements. At the bottom of it all, they are paid by their clients for running ads. Whether the news they report is factually accurate or not is irrelevant. I can guarantee you that their long term contracts for spots have zero clauses about veracity. And many clauses about make goods for unplayed ads.