For motor-only applications, the slower the motor speed, the larger the motor needs to be. Large motors could be expensive and might not fit within the allowable envelope space of a credit card applicatoin. Utilizing a gearbox with a smaller sized motor enables the unit to operate at lower speeds.
In order to understand the importance of using a gearbox to diminish motor speed, think about this situation. You have a pastry conveyor that adds cherry filling as the pastries go by. Because this is definitely a fairly light load, you would not want the conveyor operating at 5000 rpm. If it was, there would be pastries and cherry filling speed gearbox everywhere!