I think it's just a perception thing. I don't see emptying the dishwasher as part of the task that is filling it. My last task of the day is normally turning the dishwasher on and to me my task list feels finished. In some sense the tasks related to dishwasher for a day are "empty -> fill -> turn on".
You could use your same type of reasoning for food/cooking. When you buy food and put it in the fridge to cook later, you haven't finished the task. I think that's more a way of feeling permanently uncomfortable with things not being finished. There is no end state for most things in the house. Work is never done.