Many consider breaking promises to be wrong and contracts to be promises, and so consider breaching contracts to be immoral.
Many others also consider the long-term negative consequences of breaching contracts to be worse than short-term positive consequences. If they consider short-term thinking at the cost of the long-term to be immoral, they would consider breaching contracts to be immoral.
To you, breaching a contract might just be another IF-THEN which is implicitly or explicitly coded into the contract, but others consider it to have moral weight.
I agree. Back when the financial crash happened and people were walking away from their mortgages, there was a lot of bloviating about those people's moral duty to pay their mortgages. There is no moral component to it at all. Only a financial one.
If morality is determined by "do unto others as you would have them do unto you", then I think this probably is immoral. It's fairly low on the range of immoral behavior, but it shouldn't be a purely economic calculation, in my opinion.
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.
Many others also consider the long-term negative consequences of breaching contracts to be worse than short-term positive consequences. If they consider short-term thinking at the cost of the long-term to be immoral, they would consider breaching contracts to be immoral.
To you, breaching a contract might just be another IF-THEN which is implicitly or explicitly coded into the contract, but others consider it to have moral weight.