The majority of the people here don't collect single cards or "swap cards" as they're commonly called. It's got a lot to do with the fact that many people here are actually using the cards we buy, and a solitaire game, a special flourish or most magic tricks with a single card are nowhere near as interesting...hell, cuts become impossible!
But, on the serious side, the hobby of collecting singles came from the desire to own a piece of history in the form of vintage deck designs combined with the limited funds of someone who can't afford all that many vintage decks, particularly the ones in the best condition. Someone realized that for many of these people, owning a single card was enough to give them an example of the design work, and furthermore realized that the buyer gets a deal in that he's not forced to pay for an entire vintage deck while the seller also gets a deal in that he can sell a deck piecemeal for more money than he'd get selling it whole. (This was also a plus for those who obtained decks that were missing cards, which reduced the the value of the deck.) Thus, the subgenre of the hobby was born.
Sometimes you'll have collectors that also specialize in getting a single card from a deck - for example, they might get swap cards that are all Sevens of Diamonds or Jacks of Spades. Courts and Aces will often be sold at a slight premium, since they're more interesting visually and more popular among that type of collector.
If I recalled, there is a Chicago-based card collecting society that has had joint conventions with 52 Plus Joker in the past. Those guys would be worth checking out, if you really wanted to get into the hobby of collecting swap cards. Honestly, swap card collecting's not the worst idea in the world - it makes vintage collecting something that an ordinary mortal earning an ordinary salary can afford.