Fixed rate mortgages up in the U.S. -- that was unexpected

The best explanation I could come up with for why this happened is as follows...

With the Fed lowering the prime rate dramatically in the last few months, investors have started moving their money out of the bond market and into equity markets where higher returns are expected. To attract investors, bond sellers must offer a higher rate of return. Since bonds are used to fund fixed rate mortgages and the costs are now higher, people taking out fixed rate mortgages must now pay a higher rate. If you have a better explanation or something to add, your comments are welcome.