When a bank issues a mortgage, they sell that mortgage on the secondary market to make money. The buyers are usually Fannie Mae and Freddie Mac. Before 2008, the government wasn’t strict about what a bank had on its balance sheet. If a bank had $100 million in customer deposits, they were allowed lend out most those deposits in the form of mortgages and sell them on the secondary market.
When that got us into trouble in the 2008 housing crisis, the government tightened regulations and required banks maintain a higher level of reserves (customer deposits). This meant banks needed to keep more mortgages on their balance sheet so the question became: Which customers’ mortgages do we want to keep? Logically, they chose customers who were high net worth, low risk and steadily employed. Medical professionals fit that description to a tee!