In my experience, playing cards have a short lifespan. I am generally drinking some sort of alcoholic beverage when I play cards, and as the game progresses and more drinks are consumed spills tend to happen. And is there anything more hazardous to a game of cards than a really sticky deck? At that point, you've just got to throw them away.
Perhaps I should pick up a deck of these waterproof playing cards. They'll work just as well as the non-waterproof variety, I'm sure, and they have the added bonus of being washable if I get clumsy and spill a beer all over them. Alternately, I could play cards in the pool or hot tub, at least in theory, if I had either of those. But just imagine if I did!