Please explain how rental owners are not "fungible" in an economic sense?

Does it matter to me if my landlord is a big real-estate trust or a poor put-upon "family" owner with only two or three spare houses to their name?

Sidenote: you could even argue that big corporate landlords are better for society. In my experience, they tend to be more professional, and more committed to obeying the letter of the law w/r/t to tenants' rights.