It turns out that the size of the banking systems in many wealthier European countries far exceeds the total GDP of the country. Here is some summary data for the countries (most of them OECD members) in which the total of all bank assets exceed 100 percent of GDP.
Bank assets as a percentage of GDP
Luxembourg 2,461 Ireland 872 Switzerland 723 Denmark 477 Iceland 458 Netherlands 432 United Kingdom 389 Belgium 380 Sweden 340 France 338 Austria 299 Spain 251 Germany 246 Finland 205 Australia 205 Portugal 188 Canada 157 Italy 151 Greece 141
(For comparison, total banking assets in the U.S. are equal to approximately 82 percent of GDP.)
So it's no surprise that the Europeans are collectively willing to throw everyone else under the bus in order to save their bankers' asse(t)s. Why the Americans are so willing is left as an exercise to the reader.