It's simply become memetic. Why bother combing through the video for a different still when you can use the same one everyone else is?
Except in this case the Snowden image is not "content". It is an icon: visual shorthand that catches the eye and identifies the topic. In a story about a corporation, they would use that corporation's standard logo rather than a unique picture of the generic corporate campus.
All of the pictures of Snowden's girlfriend in various poses and states of undress? Now that's content.