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.
Can’t take the house with you when you die so the less you end up paying the better in a way, unless you have someone to pass it on to like kids
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.