The creditor failed that by not offering the credit at zero interest, as they would have liked to have done unto them. Why should the golden rule only be applied one way?
You are a lender of money. Someone asks you for money. What's the interest rate you should charge if you apply the golden rule? Zero, because that's what you would want to be charged. Therefore, the creditors in this case broke themselves the golden rule, and shouldn't complain that the debtors did also.