I'm not defending the White House's off-camera briefing policy by any means but how would NBC being barred from the briefings completely for breaking the rules help them as a news organization? How does that make them cowardly?
Cowardly, would be the administration forbidding cameras at the briefings.
See: https://www.washingtonpost.com/news/the-fix/wp/2017/02/24/wh...