Because in the past when decks of cards begun being produced on larger scale in factories, there were a lot of companies in this business. So to differentiate their products they started printed a logo that would represent the company on the first card which is the Ace of Spades. Also something interesting to know is that this art style was very popular in Middle Age when it was used to decorate the books that were wrote by monks. P.S.: Sorry for my bad English.