Why is there no discount for early settlement or payment by Direct Debit?

Direct debit is the most convenient way to pay. Approx 65% of Council Taxpayers choose this method and there is not a need to attract people by offering a discount.
Any discount scheme offered would be difficult to administer and only penalise those less able to pay, as it would have to be self financing i.e. those unable to pay early or in one instalment would pay a higher tax in order to provide for the reduction given to others.