But what is the marginal cost of doing that work? Could the landlord hire someone to do it for multiple apartments? How much would the value of that service be

But what is the marginal cost of doing that work? Could the landlord hire someone to do it for multiple apartments? How much would the value of that service be vs. what people are willing to pay on Airbnb? Let's be honest; marketing the place on Airbnb and dealing with renters aren't a huge value-add. The majority of the value is generated by the ownership of the building, and the building owners want to capture as much of that as they can. Airbnb is a slippery slope: it mixes the hotel markets (which tend to be much higher priced) with the rental markets. This brings the prices of rental markets up, and many renters may feel the only way they can afford their apartment is if they rent it out. It's also how you get $1 million studio apartments in Manhattan - the monthly payment on a $1 million loan isn't bad when you consider you can rent it out at $350/night for half the year (hotels in the same area are ~$500/night) and still turn a profit.