Two very relevant examples of when the "amortization" argument won't apply:
- a rising market in which the landlord bought a long time ago. Their purchase price was way below the area's current market value. So they can cover their expenses while you still pay less in rent than what a modern-day mortgage would be.
- a home buying market that's expecting continued pricing appreciation. Homeowners can (and will) rent out property at a loss with the expectation it'll be made up in a higher sale value years down the line. Whether or not this actually happens, of course, depends on their ability to accurately predict the future.
There's also the inverse case of declining markets, when landlords can end up over the heads financially and simply can't charge the rates they need to cover their mortgages, because the entire area has turned south.
There are very real financial risks to landlords. They can't just charge whatever they want. It really depends on the state and future of their market.