I think you underestimate how many people actually try to pay with contactless despite the signs on the walls, floor, and every single barrier paddle. Gateline staff at Liverpool Street do try to be proactive and stop people whenever they see someone with luggage tapping their card, but they can't save everyone. At some stations further up the GEML, people who pay contactless are sold a new ticket and told to contact TfL to dispute the charge, but it all depends on if an RPI gets to them first.Sadly GA seem more interested in penalising passengers than dealing with unwitting mistakes fairly.