There are two forms of money in the US economy. There is hard currency which the US does prints and ends up in banks as reserves (if you print it, you go to jai

There are two forms of money in the US economy. There is hard currency which the US does prints and ends up in banks as reserves (if you print it, you go to jail). There is also interest bearing form of money called the US treasury bond. The US prints and spends (though most of the printing is digital) and then sells bonds to convert some of that non-interest bearing money into interest bearing money. It doesn't have do the latter but it does because ... tradition? Also useful for large institutions to have a safe interest bearing asset. Economy likes that sort of thing.