@gazzag123 Because when you are mass-selling cards (such as when you are creating a completely different deck, for example.) And I said only rare cards. Because rare cards can only be aquired by getting 500 score or getting lucky on the slot machine. So if you sell the 1 rare card you get, you can't get it back.
I'd suggest making the are you sure you want to sell your rare card a yes/no option rather than a double click option. I was mass-selling and accidentally sold my rare...