This is an interesting question. The word "ploy" is a coined (invented) word. It was popularized by Stephen Potter, in a 1947 book, "The Theory and Practice of Gamesmanship (or the Art of Winning Games without Actually Cheating)."
A "play" can mean a brilliant move or maneuver.
A "ploy" usually means a sneaky psychological trick that has nothing to do with the actual game play.
A marketing ploy means a dishonest marketing trick. For example, a marketing ploy might ask you to fill out a survey explaining what you like and dislike about a product. The company doesn't really care what you think. They just to make you spend time thinking about their product.