Greece has already had 5 years of austerity policies that have done nothing to decrease the debt. It should have been clear that Greece wouldn't be able to repay everything they owed, but the creditors didn't want to accept such terms. Hence, the plebiscite which has now ended with an overwhelming 'no' to the creditors' impossible terms.
More: The Guardian view on Greece’s no vote: eight days that shook a continent | Editorial | Comment is free | The Guardian (5. July 2015)For the broader eurozone, by contrast, forcing Greece out will produce no upside. Instead of a negotiated debt settlement, official creditors could lose everything. A slow-burn fuse would be lit under the whole single-currency project, as markets speculate on where may be next. And now that the respectable course of EU-backed orthodoxy has failed at the ballot box, there is also a risk of political contagion, with untold consequences for the more fundamental and more precious project of kinship across the continent.