It's a lack of empathy and basic understanding of sight lines. The bar doesn't keep the pavement ape from stealing your stuff but that's what they think you're implying. It's so the cashier knows where one order ends and the next begins. She is busy scanning and sometimes bagging so he isn't watching to see the exact items each person puts on the belt. The gap between orders is too small most of the time to know that it's an implied separation. Plus people sometimes end up with gaps within their own orders. All of this is incomprehensible to the pavement ape who can't view the world from any point of view except their own.
>>513262511
Most places in the US still do it unless they're a deep discounter.