As Moises Naim says, these days power is easy to get, hard to use, easy to loose.
As complexity/unpredictability rises in any system its natual that govt will shed power. We have already seen this with setting of interest rates.
There is a long list of reasons why the Treasury Dept, President, House, Senate, Supreme Court or NASA doesnt get to set the rate.
Why did they hand over that power to the central bank? Read some financial system evolution history. Mindlessly ambitious people, the kind who run things hardly ever hand over power to someone else unless they see weilding the power puts a giant bulls eye on their head when the inevitable unpredictable/uncontrolable event occurs. Same goes with the Church or Religious institutions. Why does govt stay out of that lane? Why did Italy hand over the Vatican to the Church?