The same trick is applied to trick potential customers into going through a sales funnel and convert to a paying customer.
"There are 42 people watching this hotel right now! Only 3 rooms available for your dates! We'll murder ANOTHER puppy if you don't book right now!"
Yes, I worked for Booking.com. They don't do it everywhere, in some places it's illegal, and sometimes they simply change the words slightly to make it suggest urgency.