Coyotes and Sabres Line Brawl After Game

Oh, hockey players and their silly unwritten code! Here are some guys pushing and shoving and punching after Buffalo beat Phoenix, 2-1. I’m not 100% certain why the referees didn’t allow the players to pair up and fight. Is there a written rule about fighting after the final horn? If so, shouldn’t the unwritten rule about disrespecting something or the other supersede that written rule?