The Ace of Spades became the most elaborate card in the deck because it once served as proof that a tax had been paid. 

Beginning in the 1600s, British authorities used the Ace of Spades to show a deck was legally manufactured. When counterfeiters began forging the card to avoid the tax, officials and card makers responded with increasingly intricate designs, stamps, and engravings that were harder to copy. 

The tax is long gone, but the tradition remains. Every time you open a deck and see an oversized Ace of Spades, you are looking at a centuries-old anti-counterfeiting measure.