Why haven't countries dropped the debt?

There is one valid reason that I know of. When someone asks to borrow money and they say they will pay you back then they are likely to spend it wisely so as not to waste it and make sure that it goes to good use as they need to make a return on the money to be able to afford repayment. However when a gift of money is given the person does not need to spend it wisely because they will not need to make a return. So keeping the debt serves as an incentive to make countries spend their money more wisely. However, when you have countries with corrupt leaders this type of thing doesn't really work.