For a moment, the 50-yard line at Levi’s Stadium in Santa Clara, California, was the media capital of the world. As the San Francisco 49ers were warming up for a Sept. 21 game against the Arizona Cardinals, NFL commissioner Roger Goodell caught the eye of Neal Mohan. The YouTube CEO, flanked by a handful of his platform’s top creators, marched onto the field and embraced Goodell. About an hour or so after their meeting on the field, the moguls addressed creators and guests in a suite. “We want t...