Mortgage rates fall to fresh lows this week

This week fixed mortgage rates dropped to the lowest they've been in decades. Just recently the FED revealing a economic stimulus bond-buying program and it helped instantly seeing the rates drop from 4.24% to 4.17%, the lowest its been since 1971. Mortgage rates tend to follow lower yields for investors and they will occur when the FED purchases the $105 billion in Treasurys over the next month. Do you think there is any other reasons why the mortgage rates dropped to this all time low?