The reason fixed mortgage rates have been below inflation recently is because the financial industry (bond buyers and mortgage underwriters, at least) have largely bought the Fed's "transitory" narrative. A 3% mortgage remains profitable if inflation runs at 8% for a year and then returns to 2%; it becomes very unprofitable if inflation stays at 8%. The reason mortgage rates have climbed so much in the last couple months is because the "transitory" narrative has basically collapsed, and the bond markets are now starting to price an extended period of high inflation into the rates they charge.