Because hospitality resembles nothing else, and generalist web studios learn that on your project.
A property does not sell a product. It sells dates that expire. An empty room on 12 July is never sold again — it does not go back into stock. That changes everything: what goes first on the page, where the button belongs, which season you build content for.
Every property has signed terms with Booking.com and the other platforms. Some of those terms govern what you are allowed to say about your own rates on your own site. We know that, and we take it into account when we write the copy.
Then there is the technical side: booking engines, channel managers, overbooking, seasonal rates. That is not something you learn on one project. You learn it on twenty.