Americans are not saving their money "for a rainy day." They're not saving money and investing it.
Americans are spending their money. They're also spending other peoples money, money they don't have.
The economic crisis of 2008 is largely due to the fact that despite the fact that Americans have saved no money that can be lent, trillions of dollars have been lent anyway, to people who couldn't pay it back, and didn't pay it back.
How can money that doesn't exist be lent?
The Federal Reserve creates money out of thin air.
Congress then passes a "Community Redevelopment Act" requiring this newly-created money to be loaned to people who are not creditworthy. Not surprisingly, they default. Then the government steps in to "bail out" those who hoped to profit off these bad loans.
Creating credit to loan at interest is a bad public policy.
Encouraging savings is a better policy. It cannot be coerced, but it can be encouraged.