Because, honestly, the referendum they just called is one they know won't pass. So when it fails they then have the legal excuse to go back to the Drachma, refuse to honor euro denominated debts, and then devalue the currency to the point where people can still have jobs.
You know - the way Argentina and practically every country in history that has been in a huge debt crisis has dealt with things, because it's the only solution that works.
The real question is why Europe as a whole didn't see this coming and didn't stop giving them money a long time ago.
I mean, seriously, German bankers didn't figure this shit out when I was able to?
Oh well, I guess things are about to get a lot less expensive for me in Europe.