Putting the divider down is also polite. Why are we expected to always be the most polite or suffer cruelty if we don’t comply?

I always put the divider down behind my stuff, line behind me or no, and expect nothing in return from the people behind me. If the person in front of me can’t be arsed to put the divider down after theirs stuff, it’s fun to see how many of my iitems get scanned before they get to have the awkward conversation with the cashier. Yes I’m normal and well adjusted, why do you ask?