Someone in my extended family has had a rental house since I was a baby, long before air b&b. (It's the family gathering place; it's just rented out when no one is there.) A dishwasher was added a few years ago. They ask guests to start the dishwasher before they leave so the cleaners can empty it when they come. When guests get there then dishes are all clean, dry, and put away. If the cleaner had to load the dishwasher and wait until it was done to unload, cleaning would take longer and thus be more expensive.