Sensors trip just fine with them the regular way, which is the only way the cashiers ever position them.
The dividers far predate the sensors. There is a limited amount of conveyor space and placing it long ways would often make it impossible for all the groceries to fit. It is a privacy fence. If it weren’t, a thin stick would be the wrong shape. A half sphere would probably be better.
The only thing wrong in the first picture is the sugar free cheesecake Jello pudding. Please get chocolate or butterscotch instead!
In today’s world putting in on wrong could be a capital offense.