Jumbo loans are mortgages for the best credit risk borrowers who want to purchase mansions. In pre-corona times, lenders were falling over each other to welcome jumbo borrowers, but not anymore.

Greg McBride, the Bankrate chief financial analyst, recently said demand has dried up for jumbo mortgages as investors shift to mortgage bonds for government-backed loans where "they're assured of receiving payments even if large numbers of borrowers are in forbearance."

"Most mortgages get made by lenders who then sell it to someone else," McBride said. "If there is no willing buyer, lenders will stop closing loans so as not to be stuck holding the bag."

Tendayi Kapfidze, the chief economist at LendingTree Inc., said in normal times, jumbo loans were all the rage. Now because these loans "don't have the government guarantee, a lot of those loans end up on the bank balance sheet."

According to Optimal Blue, a Texas-based firm that monitors mortgage rates, lenders are charging more for jumbos than conventional mortgages, and this is the first time in seven years. Lenders have also tightened lending standards for wealthy households.