The increase in excess reserves is not mysterious. The Fed starting paying 0.25% on them in 2008 (now 0.50%) while other interest rates were near zero.
Eventually some minor crisis will trigger spending, all this excess cash will hit the system like a floodgate, and we will have an inflation spiral (because suddenly hoarding will be a bad idea). And the irony is that the ethical justification for the fed is that it is supposed to be countercyclical, and thus 'good for society'.
