Chocolate Covered Strawberries the Next Day
Sugar is hygroscopic and the sugar in the chocolate coating attracts the water in the strawberries. It's the same result as when you sprinkle fresh berries with a little sugar to macerate, or draw out their juices. How mail order companies manage to do it is beyond me unless they coat the berries with some kind of barrier before dipping in chocolate to prevent it or are using some kind of sweetener that isn't hygroscopic. One of the wonders of science and technology, no doubt.