Security is the reason.
This international online payment gateway that allows the use of our local card information requests those details in order to verify if the person trying to make a purchase with the card is the rightful owner, as the billing address that you are to fill in must be the same as what's registered with the account that issued that card. That information alone on some sites can authorize the payment without even waiting for some authorization from your bank; no OTP or even card pin might be needed. They are security measures that almost every site applies to card payments.