Two things: first, landlords aren’t entitled to a profit, and second, landlord input costs might be completely different from an owner resident.
On the first point, if the landlord’s costs are $2000/month, and the market rent for that unit is $1900/month, the landlord would rather lose $100/month on a lease than lose $2000/month on a vacant property.
On the second, it might be that the landlord bought the place when it was much cheaper, or has a much lower interest rate than what is available today. So if the landlord’s costs are $2000/month for a property that would now cost $4000/month at today’s purchase prices and interest rates, but can rent for $3000/month at a profit to himself.
Similarly, some volume landlords can spread certain costs around and not pay nearly as much as an owner resident. It might cost $1200 to hire a plumber to do a 6-hour job, but it also might cost $150 to simply have a plumber on the payroll to do that job, if you’ve got enough steady work that it’s cheaper to have him around.
Producing value gives leverage. A salesman who brings in lots of revenue and profit can negotiate a pretty high commission, because controlling that level of revenue/profit represents some leverage.