I don't get how selling MBS on the market will lower housing prices, housing prices are a result of demand/supply + interest rate affordability, neither of whic

I don't get how selling MBS on the market will lower housing prices, housing prices are a result of demand/supply + interest rate affordability, neither of which will be affected by selling MBS' that carry an older lower rate and don't pay out that much. I think it only results in Fed technically losing money.