Without sarcasm, given the latest purchases of assets beyond Treasuries and MBS, why do you think the Federal Reserve has purchased assets at market rates?
It's my understanding that their asset purchase programs involve just buying things normally on the open market. It's of course a bit more complicated than "market rate", since large purchases marginally affect the price, but as far as I know nobody gets a special deal where the Federal Reserve pays 1.5x what the bonds are worth.