There is no real cost of defaults.
The money that wasn't paid back was created out of thin air with no effort from the bank.
Money laundering is taking ill-gotten gains and processing them to make them look legitimate. This is exactly what the central banking system, in partnership with the government, does.
However much you try to justify what they are doing you can't deny that the banking system is charging interest on every unit of currency in existence and they created them all for essentially free.
People absolutely should pay more interest - the free-market rate. It's absolutely wrong that people who get into debt are rewarded for doing so, at the cost of people who don't, who have the value of their savings, wages and pensions stolen.
It's a vicious cycle - lower than free-market interest rates force people to have to borrow money. Look at what it has done to prices of houses relative to wages over the last 50 years. It's reached the point that many people are now forced to take on 35, even 50 year mortgages, just to buy a very modest home.
Look up the Cantillon effect.
See here for some of the terrible, far reaching effects: https://wtfhappenedin1971.com/