One reason might be to validate that the card works at all.

Another might be to bypass anti-fraud provisions of the issuer. (It seems plausible that someone trying to buy a laptop at a random retailer away from home might be less likely to trigger a fraud alert if they had a same city, same timeframe hotel reservation on the card.)

As discussed elsewhere in these comments the booking agent will likely not be processing the payment and probably won't perform validation of the details save for a Luhn check on the number.

Someone will be attempting to process the payment.

A fraudster doesn't care who that is, any more than I care who it is when I legitimately book a hotel room.