Because the hotel then has to swap the reservation whenever it's traded. Let's say I want to book a hotel in the future for downtown Chicago Cubs making it to the World Series. As the season progresses it's a future whose value goes up and down depending on how they are playing. If the hotel is in the loop they could play shenanigans and charge you a fee every time you reschedule. The idea of the blockchain is that it's out of their hands.
The owner of the room at the time of the booking shows up with the private key, and swaps it for the room key.
If you involve the hotel enshittification will ensue to make sure they grind out every last cent.
Also, being on a blockchain allows for trades such as swapping rooms across chains, trading rooms for cars, etc. The blockchain unifies ownership and rights as tradeable like money did for barter. There is a common unifying method of exchange.