An economic argument would be that a customer defaulting now will signal to future lenders that they are a risky customer, leading to a raise in rates for futur

An economic argument would be that a customer defaulting now will signal to future lenders that they are a risky customer, leading to a raise in rates for future loans. The moral framework which says that defaulting is bad is in some way codifying the economic argument, by categorising actions that will lead to future difficulties as "immoral".