> Unless you think landlords are running a charity, some part of your mortgage is going to them as profit

This isn't true due to market dynamics.

If a homeowners mortgage is say 4k/month and they list the property at 4.5k/month and receive no renters they can only do this for so long before they are forced to down the price.

Of course, what actually happens is that they list it for 5k/month because other properties are renting for that amount and that's the market price. But if supply increases in the area or demand decreases then prices will go down possibly below the owner's mortgage cost because uh getting 3.5k/month is better than 0k/month.

Maybe OP is saying when you buy from a landlord, they still get their profit (you pay them the NPV of the expected future rents - it's neutral from their perspective).

In cases like your example, what forces landlords to lower the rent? Usually only a) cost of credit, as you said b) opportunity cost, and c) government intervention [land tax, property tax].

a) not all landowners have mortgages! many own outright. they make pure profit b) the game theory of this case is frequently misunderstood, landowners are a monopoly and are strongly incentivized to act as a cartel. same principle as walmart destroying old stock.

Landownership is one of the most lucrative and profitable enterprises in (American) history, so you might want to question the logic which has convinced you that market dynamics is so effective in taking its profits.