Right. But @SnowWhiteDoc has 11 cards to keep track of. If they ever cancel the refund could go to any one of those 11 cards, whichever one was used to pay for what is being refunded. How do they see which one it’s gone to?
Someone else may have balances on 12 cards, maybe to pay DVC maintenance dues each month.
By putting in 6 cards, and if it’s not one of those, replacing with the remaining until you see which one changed. Not too much more work than if it let you put in all 11 or 12 at one time.
You can always look up the balance on a card, even without logging in. The limit is only saving them to your account, right?
Minor inconvenience, means you have to save the card info yourself, but that’s a good idea, even if it’s saved to your account.
Tracking 12 should be good enough for our purposes, between my account and DH’s. And, I guess if all else fails, the dog can get a Disney account…
Would that buy him Scooby snacks? 
She had a Mickey leash for a while