Landlords who rent at their cost and not the market price won't rent.

I don't see how your statement follows at all. I'm sure landlords would prefer rents to be higher than their mortgage but that will be determined by supply and demand, not their desires. The housing market is huge, with lots of alternatives and competition, so you can't exactly price fix it either.

You can choose to not see it, and I can struggle to explain it, but i dare you to find a landlord in a city larger than 100k who is renting at a loss.

I suspect it’s some kind of uncoordinated price fixing. E.g.

1. landlord buys property, optimistically sets rent at $mortgage+30% even tho that’s above the market rate

2. Everything cheaper is rented, or highly sought after, so renters are forced to take the higher rent.

3. Other landlords see places renting for higher than their current rent, and raise prices accordingly.

But i’m no economist. I’ve just never seen a landlord take a loss except as a result of special circumstances. Economic crashes, fire, etc.