The truth of the matter is that if Rishworth can sell the idea to the client airline that there are people out there who will work for this kind of money, then they get the job of recruiting.
The other agencies probably told the airline to 'get a life' and knew damn well that there would be few takers.
It is not the agencies that decide the salary package but the client airline, and they will always go for the lowest that they are told that they can get away with. Rishworth may be guilty of 'helping' this process, but I suspect that they are probably keen to just get any work they can along with all the other agencies.
Supply and demand is true, but when you are supplying pilots who will be miserable and demoralised during their time on site, and probably run off at a moments notice if a better job arises, then it pay's you as an agent to get the best deal, best accomodation and keep in constant touch with your crews during the contract. If the pilot performs badly that reflects on the future chances of the agency getting more work, so it's in the agency's interests to keep you happy and make sure you see the contract out.