It’s been almost 20 years since I first noticed. The first TV anchor I noticed using partial phrases in lieu of complete sentences was Shepard Smith of Fox News. Maybe he started it, maybe he didn’t, but it remains an irritating distraction, and the practice has gone on so long that now it’s ingrained in the news-writing culture.
A generation growing up with the mistaken belief that this is a complete sentence.
I think the practice was started to effect some sort of headline-speak. It certainly wasn’t to save time and use language more economically. Reporters saving only a nano-second by not using the word “are” where it belongs in this sentence.
Perhaps, metaphysically, by not using the various forms of the verb “to be,” they are making a statement about the nature of being, of existence. By not saying “is,” “are,” “it is,” “you are,” “they are,” etc., they question reality itself.
That, however, is probably assigning too much credit to those who first condoned and enabled this usage.
Easier calling it just bad writing.