Because most of them already pay their debts. Only a couple states left haven't did it.
Explanation:
At that time, the southern saw this gesture as the central's government way to assert more control to their states.
When the government pay their debts, they assumed that the central government somehow will increase their taxes as a form of repayment. This make the states who already paid their debt felt that the government use them to pay off the debt of the states who haven't pay.
