This is for getting tickets printed on the spot, not for using the already printed tickets. People buy tickets online and have it printed later at the airport/station kiosks, which lets you prove your identity abusing the fact that customers realistically don't forge a credit card. It can be an ID/password login at the busy station using unresponsive touchscreen, or a membership card of the airline/train, or maybe even a driver's license, but CC is probably the most convenient(unless...).