Another in-character reason is that T'Pau thought it was blazingly obvious that when you fight the groom at a wedding to take possession of his bride, you'd better kill him. It would have struck her as silly, as having to spell c-a-t, to mention that the fight is to the death. "This is for all the marbles. Aren't weddings done like this on every planet?"
Plus one or both of the combatants is going through uber Vulcan rage at the time so it seems a given that they aren't to likely to play nice.