Great appreciate you providing feedback. I play MTG as well so I can understand the initial reaction to playing all cards in your hand.
The reason behind that is you are meant to buy cards from the 4 Attunement Card options on the right side. Those cost you Sanity and will go in your deck to add benefits to your play. However random Madness effects like Madness cards will also trigger and thus you are now forced to play the hand you are dealt. Strategy comes from mitigating the negative effects and capitalizing on the positive effects in your deck.
Hope that clears some things up from a logic perspective.