Why has the ECB’s low-interest-rate monetary policy failed to rebalance savings and investment?

Despite a highly expansionary monetary policy since 2014, the euro zone still has huge excess savings over investment. So the ECB’s monetary policy has failed. But why? The fact the income effect on household savings seems to have prevailed in Germany and France, where the very low interest rates have coincided with a rise in the household savings rate; The fact that companies have not fully invested the fall in their interest payments; The fact that euro-zone countries as a whole have not taken advantage of the low interest rates to run larger fiscal deficits - on the contrary, in fact - which results primarily from Germany’s behaviour; The significant and seemingly irreversible decline in housing investment in the euro zone after the 2008 crisis.