If this is a serioius question, you might as well ask why doesn't the treasury just print the $trillion in bills. The last president who tried that didn't fare too well. See the way it works bud, is only Banks is allowed to print money from thin air - now shove off with your questions 'fore you have yourself an "accident."
It's a good idea. Ron Paul intended to do it - pay off the debt with Treasury money. It's basically a resurrection of colonial script or the greenback - debt-free money.