Since you do not need to provide as high a rate of return when there's high need for MBS, home loan rates are lower than they would be if the Fed weren't doing all that buying. The FOMC has direct control over something called the government funds price. This is the price at which financial institutions borrow from each other when they need funds over night. When rates of interest are greater, more people will wish to purchase bonds-- why do not greater rate of interest push bond prices up?