Like, it would count as being in your deck if the game ended right then, which is impossible.
But the card is not on my deck, it's in my left hand and I'm revealing it. While I'm deciding what to do with that card, often times I want to know how many cards are in my deck, and it's important for that number to be accurate.
At the very least, it needs to be consistent with other cards like Apothecary, Patrol, etc. which report cards in reveal-land as not being on the deck.
But the card is not on my deck, it's in my left hand and I'm revealing it. While I'm deciding what to do with that card, often times I want to know how many cards are in my deck, and it's important for that number to be accurate.
At the very least, it needs to be consistent with other cards like Apothecary, Patrol, etc. which report cards in reveal-land as not being on the deck.