Ah! I jumped straight in hard mode, I didn't notice easier difficulties would change the copies limit.
Thinking about it more, the Boredom already penalizes you for having multiple copies of a card. I thought the card limit would be 2 on all difficulties because adding a 3rd Fondle is shooting yourself in the foot. There's only a few cards that can benefit from more copies. The Fingering and Fuck cards have their Dildo equivalent already, it's only Take Off Her Clothes that runs into that issue because it is necessary, has no alternative and doesn't care about Boredom.
If the Hard difficulty limits you to 2 copies intentionally, the duplicate cards rewards make sense. You can still win the game despite it, the Retry Bout lets you recover from terrible stripping RNG.