Those mortgages have an interest rate of less than 3%, but now the returns on even low-risk investments are higher than that, so the borrower is better off investing the money, using some of the profit from that to pay mortgage interest, and keeping the rest.
Those mortgages have an interest rate of less than 3%, but now the returns on even low-risk investments are higher than that, so the borrower is better off investing the money, using some of the profit from that to pay mortgage interest, and keeping the rest.
Even more: an interest rate of <3% is basically blown away by annual inflation.
That assumes your salary goes up with inflation, though.