America’s largest home lender harnessed a generation of low rates to refinance millions of mortgages. Its effort to switch focus is a challenge. The mortgage industry turned from feast to famine faster than America’s largest home lender anticipated. Rocket Mortgage harnessed a generation of low rates to refinance millions of homeowners. Last year, it racked up more than double the refi volume of any other lender, accounting for more than $1 of every $10 lent out during a boom for the mortgage industry. Now the Federal Reserve’s efforts to fight inflation have sent mortgage rates soaring. And refinancing, the driver...