Probably because they can get away with it. I bet most teams would prefer to remain vague on injury issues, but some leagues more or less mandate that they give up the information and they are followed by a huge amount of media that wants to break the news. Most NHL injuries involve a guy (barely) skating off the ice and going to the dressing room never to be heard from again. In the NFL you have 14 different angles of close-ups, the guy goes down on the field and gets taken off by a cart and Schefter/Glazer types race to break the exact news. The NHL has never forced their teams to be open, and they are followed by a handful of Canadian reporters who respect the tradition of not releasing that information. Exactly. NFL coaches would love it if they could get away with not releasing injury info.