Sitting implies to other people that you're lazy and lack a work ethic, because anyone with a drive wouldn't be a cashier. In reality people just need a couple moments relief from the back and foot pain. Not even slightly taking some weight off by leaning against a stool is permitted.
This type of perspective can easily start to infiltrate technology. Someone already made a comment about how they thought this would be about managers forcing people to use standing desks. Do you want to be passed over for a raise by management because you sat down at work while coding for most of the day, compared to co-workers using a standing desk?