Around Germany and Greece there were other countries. They went by names like frugal four and PIIGS. They forced "austerity" and stricter working hours onto indebted countries to save their own banks.
The colours on this map show well that northern "productivity" is not about working hours, but about other topics that did not get addressed. Among these topics are also tax heavens (think the Netherlands) and money laundering (think Austria's special relationship with Russia).
So it was nothing more than poor political leadership without vision.
And that's all stuff that reflects on productivity.
Take two factories making the same thing in Germany and Greece, evaluate the productivity per work hours, one is lower, compare different things in both factories to point to what can change in the one where productivity is lower to make it as productive as the other one.
The less productive one gives no breaks except for lunch to their employees? Try giving them more breaks. The less productive one has older technology? Update it.
The point isn't to find who's responsible, the point is to find what works in one place and seeing if it can be implemented elsewhere.