Lending it into existence is how the "money" gets to be what is known as "monetized" in a debt-based monetary system.....the fact that it has to paid back with interest makes it "worth" something to those who have their own debts to pay back.

If they truly just "printed" it, it would be like monopoly "money"....at least in the quantitys they would need to produce it in anyways.

Now, if you get rid of the "debt-based" part, it might be different. The "US notes" you refer to......but the fed won't accept them as payment towards the existing debt.