Actually, Willard scheduled a title defense against Fulton, but as a result of the World War, authorities prevented the fight from happening. In the meantime, Jack Dempsey beat the number one contender Fulton in lightning fast fashion, which set up the Willard-Dempsey fight once the authorities would allow it.
This is apparently true but I find this perplexing on a number of levels. Also given federalism and Canada I'm very hesitant to put the blame on the authoritys. Also that fight was originally scheduled years before WW1 although at that time it wasn't as obvious or needed a matchup.