Food Delivery Driver Observation

I have been delivering food orders for a couple of weeks now and have noticed something that I have not seen in other industries that I have worked in.

While waiting for orders at a restaurant, I have noticed that drivers have a dour, sourpuss expression on their face. One time a fellow driver looked at me so I smiled, nodded my head and said, "hi". He completely blew me off and ignored me.

Look, I know that food delivery is a job of last resort for many of us (myself included) but how about crack a smile once in a while. Maybe this is one reason why there are no tip/baiting customers.

Has anyone else noticed this?