I don't buy it.

If they had an API Booking would not likely return their data to you, they would almost certainly have an API that you would search and which would then return the same result you get on their website. Probably with some nice JSON or XML formatting.

Booking makes a small amount of ads, but they are paid by the hotels that you book with. And yes, today they already have to compete with people who go there see a hotel listing and go find the actual hotel off-site. That would not really change if they create an MCP.

It might make it marginally more easy to do, especially automatically. But I suspect the real benefits of booking.com is: A) that you are perceived to get some form of discount and B) you get stamps toward the free stay. And of course the third part which is you trust Booking more than some random hotel.

I actually think it would be a good idea for Booking to have an API. What is the alternative?

I can right now run a Deep search for great hotels in Tokyo - that will probably go through substantially all hotels in Tokyo. Go to the hotel's website and find the information, then search through and find exactly what I want.

Booking.com might prefer I go go to their website, but I am sure they would prefer above all that you book through them.

In fact I think the idea of advertisement is given above impact here, possibly because its a popular way for the places that employ the kind of people who post here to make money, but substantially all businesses that are not web-based and that do not sell web-based services for free don't make their money through ads (at least not directly). For all those places ads are an expense and they would much prefer your AI search their (comparably cheap to serve) websites.

Basically, the only website owners who should object to you going to their website through an AI agent are those who are in the publishing industry and who primarily make money through ads. That is a small number of all possible businesses.