Complete speculation, but it's one of the few things that the majority of my accounts share. The accounts can be completely different, made at different times, and doing different tasks, yet all of them with the same payment info get banned.
I need to do some independent testing to see if there really is any water to this theory. As a single example, I made an account last week with my PayPal instead of my CC and it has NOT been banned yet. It has been using the same botting schedule and script as previous accounts that were banned.