throughput, throughput, throughput. Magstripes tend to work not so well when you have the ticket in your pocket for a couple days, printed codes involve people

throughput, throughput, throughput. Magstripes tend to work not so well when you have the ticket in your pocket for a couple days, printed codes involve people futzing with cameras. You can use a sort of card ingestion system to line up a QR code or the like... but those things are complicated and break down a lot! You end up needing staff to constantly be opening it and unclogging it. This works alright if you have like 6 turnstiles, less so when you have 2 or 3. Obviously you can work with those models anyways, and plenty of transportation networks do! But if your rush hour involves moving a million+ people, you really do need this stuff to go fast.