They are literally creating money that doesn’t exist to buy those bonds. They are creating liquidity out of thin air - it is literally the definition of MMT. Go back to school.
Out of thin air? The money that they are creating is based on the value of the American economy, its infrastructure and the talent of the people that created it. It allows the payment of current debt for a short period for the creation of that infrastructure. The American economy and the American infrastructure has a value far in excess of the money being printed - especially given that it will be almost literally the only game in town once the virus crests. This maintains the economy and preserves the infrastructure and the payments on that infrastructure until the short crisis is passed. It keeps it ready to launch again - without this, the entire system - and most importantly the financial system that feeds it - does collapse. So put your labels wherever you want to...and beat your hobby horse...but if you really want to kill the American economy, your method would do it almost immediately.