The vast majority of landlords doesn’t do any of that. They just pay for it to professional people from the revenue that they get from renting the house. The only labor that they perform is maximizing rent and minimizing maintenance costs (usually at the expense of the renters) and having to find new tenants from time to time.

The majority of the revenue is simply achieved by having the asset or capital to acquire said asset. They don’t really provide any service that wouldn’t exist without them, they are simply exploiting an asset and people that need a place to live.