You get insurance to manage risk. You factor in roof repairs, vacancy rates when determining rent meanwhile your property value over the last 10 years in most places around the world have at least doubled and more.
Doesn't mean the next 10 years will see that growth but if you believe your country/area's population will grow it is probably a good investment for now in the western world.
Insurance is not free money and you can't simply distribute risks among your tenants because the risks are correlated.
Like I said, you can tell it doesn't work because these businesses don't exist. There are essentially no landlords who own multiple single family homes. They do exist for multifamily and commercial.
I know plenty of people who own multiple houses. And plenty of houses that get rented and paid to the owner/landlord.
Insurance is not free money its a pool of money gathered from monthly payments together to offset risk. You don't need to distribute the risk over all of your homes you buy a policy for each home.
This stuff is 101. And works all around the world. There is even an app called airbnb that will find short term rentals for your house.