Does a government have the incentive to default on its debts?

The 10 year US bonds and the 10 year UK gilts are two assets which are considered to be risk free, their yields have been widely used as risk free rates. These two government bonds are considered as risk free assets because the two governments both have long and good history of borrowing and the two economies are large and important in the world economy. Meanwhile, other government bonds are not considered as risk free, some governments have very volatile bond yields in the global market, such as the Turkish government bond yield, the Argentina government bond yield. However, does a government have voluntary incentive to default on its debt?

In general, a government does not want to default on its debt, unless there is no other way to continue its governance of the country. Firstly, a government defaults on its loan would only make its future borrowing more expensive. Secondly, defaulting on government loans will influence government's credibility, which determines the value of fiat money; therefore, an economic instability will be created. Thirdly, a government defaults on its debt could cost the political career of the politicians and the ruling political party. The potential costs are much higher than the potential gains from defaulting on government bonds. Therefore, any stable and thoughtful government and leader will not default on its debts.

However, it is not new to see a government to default on its debts. There are some cases when a government has to default on its debt. Such cases can be categorized into two categories. The one category is economic instability and unsustainability. The other category is political instability and discontinuity.