The bottomline is that government surveillance - that is surveillance by
any government, be it the German or the American one - is a touchy subject for at least some Germans. It's no concidence that aside from Sweden, the Pirate Party had its biggest electoral successes here. It was for this reason that the Snowden disclosures were a pretty big deal around here. Last June, Obama was in Berlin and assured that no spying against Germany was occuring anymore. This means that Obama was either lying or he's unable to keep his own intelligence agencies under control.
For more than a year now, Angela Merkel has been criticized by German opposition parties and the German media for being
too soft on America regarding this issue. And this is why the CIA station chief is expelled: to restore the credibility of her government.