For one thing, the whole reason the Eurozone has these sovereign debt crises is because while the countries share a common currency, they don't share a common Treasury. So it is literally possible for a country to just run out of cash. That can't happen in a country like the U.S. or the U.K., which are capable of creating their own money.
And then even beyond that, the single monetary policy isn't helpful. The periphery needs much more stimulus, whereas Germany is worried (perhaps fairly) about bubbles, as everyone rushes cash into its borders. Plus, Germany has virtually no unemployment, so it sees no need for stimulative measures.
Economist and professor David Beckworth looked at the big picture on Monday, pointing out how the system needs some serious structural reforms to function properly.