The point is why should people who got in to debt be given money to pay off the loans, when no such provision is being suggested for nationals who didn't spend the money in the first place.

Wouldn't it be more fair just to give them all a lump sum payment?

It's effectively rewarding imprudent behavior, and penalising sensible risk taking. In the long run it will just encourage all nationals to spend money they don't have so that when they go in to debt the government will feel obliged to pay off their loan.