That doesn't really make sense to me. The homes you rent are owned by the landlord and they need to pay the mortgage and make a profit.
One might want to speculate on the future price of the property. So instead of having empty the property they just rent it. This is obvious in the west coast where rent is so much cheaper than monthly payment of a 30yr mortgage.
Other landlords use property to just launder money. So any income is useful.
OP mentions the cost of moving when you get kicked, and perhaps the "anxiety" cost, when you get a message on January 1st, asking if everything is okay, and he is thinking about selling the house...
I think you misinterpreted that comment. "They need to pay their mortgage and make a profit" is meant to by a cynical take on landlords.