Mortgage Blog

A few reasons:
1)Bond does not change too much, but MBS bond may changes.
Especially at the current market when the Fed is purchasing
MBS(till end of March)

2)Even if the MBS does not change, the lender can lower/increase
their profit magin to lower/increase the interest rates.

3)If the lender's pipeline is almost full, even the MBS does
not change that much, the lender can still increase the rate
to alleviate the pressure of more loans(that means the lender
will have huge margins if the borrower still wants to have
those higer rates)