The other reason is a relationship with different countries, which means if a country has a strong relationship with a country and between them there comes a clash, then the exchange of their export and imports between the countries stops. So, this should be also a reason.
The third reason is the country's increasing population if the population of a country increases then they don't want to pay their dept.
Because there will be more spending in a country on their health care, the security of their country, the pensions they are offering to its country's people, etc. So, I think these will be the reasons for the countries which have, but they didn't want to pay. There will be many more, but I have discussed some here.
Btw I don't understand this debt thing: Greece, Italy and Spain have one of the highest debt burdens but people from my country immigrate to work in those countries while my country isn't in debt burden. This makes me to think that debt isn't as bad as they say. The only country where life is bad is Brazil from list.