Contrary to Keynesian theory, the economy is not a machine that can be primed by increasing the flow of fuel, which is money. An economy consists of billions of people, making trillions of decisions, based on their perceptions and their values. It’s way too complicated to be controlled by bureaucrats.
I think Bernanke did what he did because he has some hope that Obama will reappoint him rather than appoint Yellen. He is currying favor w/Obama by doing what Obama wants done, and protecting Obama’s Dem party from a falling stock market prior to the mid-term elections.