Also, why can't sites display your card number in groups of four digits just like they're shown on your card. This makes it much easier to verify your card number for people with poor eye sight. Some sites do, most don't.
So you need to pick your poison:
Either ask people what kind of card it is and then group their numbers nicely ... or don't ask them what kind of card it is (since you can tell anyway by the numbers and schema) and have ungrouped numbers.
I prefer the latter, actually, since it annoys me to be asked a question that the site can infer the answer to ...
Building in accessibility is a net win to all users, even those who think they may not directly benefit, spacing things out in a reasonable and predictable way helps everyone and especially those with eyesight, memory, and attention issues.