Most of loan originators don't hold the loan on their balance sheet. They just package your loans and sell them to investors on mortgage back srcurity (MBS) market. Last week, investors are so scared and stop buying MBS and cause the rate shoot up even when treasury rate dropped a lot.
This is similar to money market seize up during 2008/9 crisis. Fed is worried so much that they felt they have to intervene to avoid the collapse of housing market.