In the world of hockey, when a team wins the Stanley Cup, they usually put the names of their players on the Cup to honor their achievement.
Due to injury issues, Patrick was unable to hit the ice for a single match this season and in the playoffs. This means that according to official rules, the Golden Knights don't have to put his name on the Cup.
Also, every champion teams can only write 52 names on the Cup, including the staff and the players. They've decided to use his spot for someone else.