Technology Connections on Youtube has a rather good video on the subject: https://youtu.be/_rBO8neWw04
Dishwashers also save water by only drawing in enough to run half the jets at once. They then switch between which half is active which works just as well for washing but takes twice as long. I don't think many people sit there waiting on the dishwasher so it really doesn't matter that much if it takes 3 hours instead of 1.5h if it means less cost.
The reason commercial dishwashers run so fast is that they sanitize dishes, but do not remove food from them. That is done by a restaurant employee. Home dishwashers include soaking and scrubbing to remove food, which takes longer.
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