The reasons are many and complex. Here are some basics, heavily simplified and without detail.
Money: The German ordo-liberal economic miracle came to a crashing halt with reunification. The DDR was broke and had no chance of being economically self-sustaining, so the BRD had to prop up the DDR. This crash coincided with an economic boom in most of the rest of the world and the loosening of credit restrictions (Clinton administration/Greenspan), so Germany was able to borrow and trade its way back to a budget surplus and profit. During this period Germany bent or broke many EU rules regarding borrowing, balanced budgets, etc. When the situation was reversed, the same leniency Germany showed itself was not extended to Greece, Spain, Italy, Ireland, anyone. Quite the opposite in fact.
Germany is heavily exposed to the derivatives market and Deutsche Bank alone is exposed to the tune of $75 Trillion, or 20 times German GDP. Now, DB is in crisis. Lawsuits abound, accusations of money laundering, manipulation of the LIBOR and metals markets, chronic board decisions (Jain/Fitschen, buying Postbank) and a failure to turn a profit in almost a decade. The bank, which is systemically important, is in utter chaos. (Shareholder meeting today btw, should be fun).
The German government’s treatment of Greece. It’s utterly criminal. So much so in fact that even the IMF finds it distasteful and won’t be party to it anymore unless there’s debt relief. This is just the most glaring example of many.
Politics: Germany is the de facto leader of the EU. The EU was, in many ways, constructed purely to stop war in Europe. It’s a kind of crappy update of The Hanseatic League. Germany was supposed to be the economic powerhouse and the French were going to handle diplomacy. It didn’t turn out that way though. Germany exerts enormous authority through the use of “Soft Power”. This means the use of sanctions, embargoes, incentives. Carrot and stick, instead of weapons and armies. This has meant keeping Turkey out and bullying the other member states.
Refugees: As most EU states struggle in the face of mass unemployment, unmanageable debt burdens and a host of other social and economic problems, Germany and Merkel threw open the borders to a mass influx of refugees. This was not her decision to make. It stinks of a wretched attempt at atonement for the Holocaust. Maybe Germany can afford it but nobody else can. Many nations struggle to feed, clothe and care for their own populations, they can’t afford (politically or financially) to care for refugees too. This is pitched to the public as everyone’s duty. It’s not. Every nation must care for its own people first, this is axiomatic. Then there’s the fear of terrorism/fundamentalism. The fear of what’s viewed, rightly or wrongly, as an alien and hostile culture. Will this lead to Sharia law in Europe, Islamic theocracies, a destruction of indigenous and already fragile native European cultures? Nobody knows, but the fear is there. So, Nationalism rises, as do right wing movements, such as Pegida and the AFD. Borders are closed, fear and antagonism are rife. Germany is blamed. This blame is correctly apportioned, your government has no clue what it’s doing. There’s no effective political opposition in Germany and Angie neutered her party opponents years ago. So, for the moment, we’re stuck with Merkel, the grand coalition and their woeful decisions.
Media: Your media just lies to you. Non-stop. I work 2 weeks out of every month in Germany. The state of the world and Germany’s position within it, is grossly misrepresented. You’ve been told everything’s fine. All cool, nothing to see here, Muslims don’t molest women, or rob people and everybody loves Germans. It’s bullshit. Your media are just wholly owned subsidiaries of the governmental and industrial vested interests.
Sorry for the wall of text and the lack of nuance but this is the best I can do at short notice.
For what its worth, I love Germany. However, the population is largely kept in the dark about reality.