Playing card games has social benefits and leads to learning and all, but playing around with the cards themselves leads to dozens of things too! Compare aces and art from different decks. Consider the manufacture of cards, the traditional colors, the etiquette of card tables, shuffling, cutting, directions of play.
Cards connect to history, art, statistics, logic, geography, religion, law, entertainment, paper manufacturing, printing technology... well they don't connect to more things than everything else does, but they're an easy way to see how things connect!
Image from a Wikipedia article.
Other images and fun trivia are here: