1. The Greek labour market is inefficient. That is why so many people work in small (inefficient) shops. Closed shop regulation for many professions lock people out of high wage occupations. Next to Portugal's 28% high school graduation rate [1] Greece's recent progress (2. Doing business is tough. Here is an anecdote from a financial commentator in Athens:
"My friend explained that the owner of the bookstore/café couldn’t get a license to provide coffee. She had tried to just buy a coffee machine and give the coffee away for free, thinking that lingering patrons would boost book sales. However, giving away coffee was illegal as well. Instead, the owner had to strike a deal with a bar across the street, whereby they make the coffee and the waitress spends all day shuttling between the bar and the bookstore/café. My friend also explained to me that books could not be purchased at the bookstore, as it was after 18h and it is illegal to sell books in Greece beyond that hour. I was in a bookstore/café that could neither sell books nor make coffee." [3]
3. The government used cheap loans not for infrastructure or reform, but to pay public servants and build a military.
4. The government lied about its finances and is depravedly corrupt.
[1] http://m.upi.com/m/story/UPI-16361301069117/