I used to think that photojournalism was predominantly driven by content, but there is much more to it these days.
Subject matter -- the story the image tells -- is absolutely near the center of what photojournalists do, but as the field matures and the aesthetics of image-making becomes increasingly precedent, there is another deeper foundational element at work here.
Although the storytelling qualities of photojournalistic practice remains high, I think that the process begins and ends with the characteristics of light.
In other words, the intensity and direction of light can make a story come to life. I think this why photographers seek out the sweet light of early morning or the subtle tones of a sunset.