It's probably called dark because the user is often 'left in the dark'[0] about how to use the interface [0] https://idioms.thefreedictionary.com/left+in+the+d

It's probably called dark because the user is often 'left in the dark'[0] about how to use the interface [0] https://idioms.thefreedictionary.com/left+in+the+dark https://idioms.thefreedictionary.com/left+in+the+dark