None of the overheads I'm thinking about lend themselves to economies of scale.
I'm talking about things like:
* Admin costs (contracting, etc.)
* New tenant costs (marketing, agency fees, reference checks, credit checks, inventory, etc.)
* Landlords' insurance
* Extra safety checks (e.g. annual gas safety checks)
* Cost of downtime between tenants
* Cost of rectifying wear and tear (cannot recover from tenants)
There's also a difference in terms of maintenance. If I'm an owner-occupier and something breaks, I can live with it for a while, shop around, get a few quotes, and get it fixed at my leisure.
As a landlord, if something goes wrong with one of my properties I have an obligation to repair it as soon as reasonably possible.
Then every now and then you get a tenant who completely trashes a property, causing damage far in excess of any deposit, and which you're unlikely to ever recover.