Expanding economy is linked to credit, which is debt. Credit is created by printing money. Credit defaults happen at the end of a recession because all the good debtors are spent and banks have to loosen in order to keep growing. Eventually loans become riskier and riskier to the banks. Meanwhile the Fed keeps printing money to expand the credit, devaluing the dollar along the way.
Currently they are printing money at a record pace. They're kicking the can down the road and opening the door for high (relative) inflation and a hard economic crash. But sure, there are no real problems with "infinite cash".