It’s kinda like the debt to income ratio the banks use for home loans. What does it matter that I make x dollars, if I only take home .5x dollars then that is what I have to pay the mortgage with. Of course using x instead of .5x works in everyone’s favor so nobody rocks the boat. I guess you could say nobody ever pays off their home either they just move up and buy a bigger one or take out a second but the fact is there are many homes that are paid off.