German banks have substantial exposure in Greece and other troubled Eurozone countries, through bonds/loans. Those bailouts (and we're getting a little vague here) are often used to service these debts, allowing said banks to report a profit and pretend their investments were sound in the first place.
Interesting that we rarely look at who lent Greece such vast quantities in the first place.
Now I'm not too much of an economist. But I would be annoyed if my money is used to bail out somebody for mistakes they made.