When I was a kid, "Breaking News" was only used for urgent announcements that had to interrupt something else. If the story about the kid who did the nice thing had to be cut short because there was another school shooting, that was breaking news.
That seems like it was such a long time ago. Now it's pretty much just the TV equivalent of clickbait, it doesn't mean anything anymore. They just put it in front of all the top stories indiscriminately.
When did it change?
It changed because they need to reprogram you quickly. You have to be mad at some new thing they tell you to be mad at.