Updated: Jun 12
There are no incentives to pay off the debt. Representatives are elected for a term or two. It is in their best interests to get as many projects financed as they can so they can bag as much as possible. They know very well that none of them is individually responsible for the fulfilment of the debt. Their successors will inherit the problem, who will think the same. In this way, the debt will likely never get paid off. The country will eventually go bankrupt.
In an institution or a group, responsibility gets diluted. A country can not afford to take on debts it will never fulfil. Therefore, democratic governments should not have the ability got to take on debt on behalf of the nation.
In comparison, a monarch can raise debt, though not recommended, because he owns the nation. The nation is his property. He would not want to lose it to the lender. Here's a related post I made on LinkedIn two years ago.