If you find out, let me know so I can punch them.

Good question! It’s actually because cashiers sitting down appears lazy and unproductive to the kinds of customers who would complain about that sort of thing! Americans generally can’t accept when retail people don’t look like their job is excessively hard, so cashiers aren’t allowed to sit. It’s been shown that standing for so long, even on padded rubber mats many cashiers have, has a detrimental effect on the knees.

The American retail atmosphere is very different from most other developed nations. I’ve heard Americans describe grocery cashiers in Europe as “rude” and “lazy” because they get to sit down and they don’t have someone bagging your groceries for you. I’ve seen many Europeans genuinely shocked at how aggressive and in-your-face American retail employees are and even more surprised to learn we’re forced to be that way by our employers. Hired spies called “secret shoppers” are used to assess the quality of service, and at any time if you don’t greet and question every customer, if you don’t constantly have a smile on your face, if you’re sitting down for any reason, you could get fired. It’s a constant system of pomp and circumstance awash in paranoia meant to put us in early graves.

This system is seen as desirable by the people in charge because it ostensibly gets more labour out of people for the same salary and it drives many to quit. It’s much, much cheaper to hire and train new people and use them up than it is to pay the wage of someone who’s been with the company a year or two.