NHL / TV will not want 2 Game 7s played at the same time. They want to try and maximize viewership.
Plus if both Western Conference series end tonight, they have more options for when ESPN/ABC/or TNT would want the time of the Rangers game to be played.
If 1 Western Conference team plays a Game 7, it would probably alter the time they want to play the Rangers game, do they want the game the Rangers game at 3 then lead into Vancouver or Vegas at 8:00? Do they want Rangers at 1:00 and lead into Western Conference Game 7 at 5:00?