Don't you know that they get a monetary kick-back for booking these rooms?
Based on my admittedly limited experience with the Rooming Department at a large convention one summer, it isn't money they get; but they do get free rooms, which they can then use for VIPs. This is a common practice in the hospitality industry and any large convention makes the same deal; they book a bunch of rooms and the hotel provides a suite, which then goes to the visiting keynote speaker or some such. This is why the rooming arrangement is so important to Rooming. But when hotels learn they can fill the rooms without offering any free rooms to the WTS, they quickly drop off the list. Of course, this can only happen if large numbers of "brothers" stop listening to the Society's command not to book a room at any place that isn't on the approved list.
The fact that so many of these "choice" hotels fill up without benefit of WTS sanction simply means JWs are like everybody else; they put individual comfort and convenience first. When you attempt to totally control people, they will exercise their own discretion every chance they get.