After Paying $1 Billion In Interest, Is SNB Going To Shock?

Swiss banks paid nearly $1 billion in negative interest rate fees in 2017, a recent Reuters report notes, pointing to wealthy bank clients largely storing their cash on the sidelines and, thanks to negative interest rates, paying for the pleasure.  In fact, the cash levels rival that seen in the wake of the 2008 financial crisis. With the cost of holding cash been at historic high levels – typically banks paid interest on deposits, not charged it -- why do interest rates remain negative in the wealthy region that abruptly left the Euro currency union in January 2015? One can thank the Swiss National Bank run by Thomas Jordan, but what is the reasoning there?