I'm not sure I follow you. Most of the houses I've rented were fully paid off so my rent (- minor expenses) was net profit for the landlord. Sometimes it was th

I'm not sure I follow you. Most of the houses I've rented were fully paid off so my rent (- minor expenses) was net profit for the landlord. Sometimes it was their sole income stream + retirement. But even if the house is still on a mortgage, and my rent is less than their monthly payment (say 80%), it still means they're buying their house at only 20% of its cost. 40 years later, they can resell and get all of that money back too, even if the house did not appreciate.