https://www.one.org/international/issues/debt-cancellation/
http://www.huffingtonpost.com/marcelo-giugale/does-debt-forg...
Countries pay back loans because they like to keep a good reputation for future loans, but this does not work in a situation where there is nothing to lose since you can't service loans anyway.
(Of course banks can enlist other states to do strong-arming: See eg Greece who were pressured to accept a deal worse than default to benefit foreign EU banks)
how are they being pressured?
> What would you use it for? Buy olives?
No, of course not. What government sells olives ? You'd use it to pay Greek taxes. Those you'll pay anytime you want to buy anything from Greece.
So it doesn't matter if export companies get paid in Euros, Dollars, or anything else. They'd still owe taxes in (presumably) Drachma and that would create a market for Drachmas.