The point is that the other player may wonder: "why are they warning me about that rule right now? Do they see that based on how we are playing, someone is goin

The point is that the other player may wonder: "why are they warning me about that rule right now? Do they see that based on how we are playing, someone is going to misplay soon?" That leaks the players information state. Proper Hanabi is played with AI, who can't feel how boring the game is when played correctly.