Presumably they have dozens/hundreds of workers to manage those units? I'm not sure how "number of units owned" is indicative of easiness. A quantitative trading firm has billions of dollars under management. Does that mean it's even easier to be a quantitative trading firm?
Correct... which makes being a landlord exceptionally easy. All you have to do is have enough money. There is no cognitive or physical load that a landlord is required to carry, you simply open your checkbook.
A landlord never loses their money because they own the land. If a resident trashes their place, well they have insurance for that, better call the contractors to fix it up.
So you don't even need to know what you own as a landlord, you just pay other people to know it for you!