The short answer is, NFC only provides a brief packet of data - the details you would see on a physical card then the vendor’s machine takes the money from the customers bank account. Payment with a QR code requires your phone to actually interact with your bank and transfer the money from your account. The reason why one is more common than another in different locations is historic. In western countries you’ve been able to pay by card at most retailers for several decades. Originally there was a magnetic strip on the card, then a chip on the card, then the card did NFC. That being the case phones could just emulate cards by doing NFC and you could pay for things with your phone. Vendors didn’t need to do or change anything. In South East Asia (and elsewhere?) that’s not really the case with many smaller street vendors requiring cash payment until recently. Many people might have cards but they were really only used for identifying yourself at the bank or cash machine. Even in larger cities, smaller food vendors often required cash payment - at least up until covid. That being the case there was never an era where people carried and used bank cards, so QR codes are the alternative tech.