Honestly, I never understood why a mortgage would even exist at, say, 3% interest ...
Why would anyone loan out trillions of dollars at 3% (that also includes the risk of default).
The same money in an index fund produces 7% over the long term
Even at a 7% rate mortgages appear to be be less liquid, more risky, and will underperform the market.
Mortgages exist probably only because the govt backs them (aka, taxpayers are on the hook) and allows banks to keep charging bogus paper filing fees on top of it. Banks offer mortgages to charge a 1K "origination" fee ... or whatever it is called.