Have a look at this article from the Jubilee Debt campaign.
In simple terms, banks and others lent money to the Greek government. They should perhaps have known better but they took the risk.
The “bailout” of the government means that these banks and others have been paid off and instead the Greek government now owes other countries. And Germany (and others) are saying that these international debts will have to be paid.
So instead of banks and other lenders suffering because they took a risk lending to Greece, many have been paid off in full with no risk. And some banks which were not paid in full have gone bust and the Greek government has had to pick up the pieces by borrowing more money.
And the debt has not gone away but will have to be paid off by the Greek people.
So who has benefited from the “bailout” given to Greece?