Plastic doesn’t dry in the dishwasher as quickly as glass or ceramic because plastic doesn’t absorb as much heat as those denser materials. Dishes made of plastic remain cooler than those made of other materials, so any water on plastic in the dishwasher is less likely to evaporate than water on the warmer surfaces of glass and ceramic. Also, most plastic cups, dishes and utensils are made from a material called polyacrylate, which repels water molecules, making water less likely to be absorbed and instead remain on the surface.
More about dishwashers:
The average person is estimated to use 10 to 15 times more soap in a dishwasher than is recommended by the manufacturer. The excess soap can build up on dishes and cause film.
Modern dishwashers tend to emit less heat than previous models, making plastic even less likely to get completely dry in the dishwasher.
Dish washing accounts for about 2% of all indoor water usage in the US. Dishwashers use about 6 gallons (22.71 liters) of water per load, and washing dishes by hand is estimated to use an average of 20 gallons (75.71 liters) of water.