My guess is this: Booking.com already knows that they are fighting a losing battle against AirBnB. So instead of trying to win it seriously, they go to make the biggest profit they can out of their situation by strongly focussing on the idiots. With idiots you have two advantages:
(a) they stay anyways no matter how shitty you treat them. They have different reasons but one of them is that they are simply used to your service and don't want to learn a new one.
(b) they believe at least some of the stuff you put on these websites.
(c) in exchange for not feeling like a total loser for a moment they are willing to pay more.
For an observant booker this website is really less and less useful. For once you can try the alternative and get a much better experience, and on the other you can often just book a room on-site after you arrive. When Booking.com just hands out a reserveration without prepayment don't think the hotel wouldn't give your room to someone else if enough customers arrive at their desk first. Money now is better than (maybe) money later. The only exception may be when you go to the big fair of your industry and the whole town is booked out.