The point is that 2.8% is likely to be a lot less than the investment returns you’d be forgoing by putting money into paying off the mortgage early. In addition, if inflation runs at say 2%, you’re de-facto only paying 0.8% interest. Finally, you may be able to get a tax deduction for your mortgage interest.

Overall, depending on the particulars, you may end up actually making money off your mortgage on an inflation-adjusted, after-tax basis.