Go back to the example of the butcher and the baker. If the butcher buys $1 worth of bread from the baker buys $1 worth of meat from the butcher, then you have $2 of GDP for $1 of money supply. If the butcher buys $1 worth of bread but the baker sticks that money in his mattress, then you only have $1 of GDP for the same $1 of money supply. Adding $4 to the system does nothing to support growth unless the baker starts buying meat from the butcher. It just makes the $1 loaf of bread cost $5.
The baker goes out to buy a new American made truck and gets his house painted by Americans because the economy is good and psychology and politics play a huge role in confidence.