It's a great business model, tbh. Because their schedule is only released daily, it leverages the interest in their most popular SP's, and creates traffic, and will have a trickle down effect for the rest of the roster. Any client who wanted to see a particular SP, especially if she is popular and gets booked quickly, would have to be on their site refreshing to check for the schedule when it is released everyday, to have any realistic of a shot. And if they end up not being able to book that particular SP, they are likely to move onto their next best choice, and so on. The more traffic, the more likely you will find prospective clients to match with whoever is working that day, basic math.
I won't begin to pretend to know all the inner workings of how to run an agency, but my guess is that when you run an agency and obtain a high rate of bookings for SP's, they will take notice, and popular girls from other agencies will migrate to that agency. Success breeds success, and if SP's can get fully booked, they can list their availability for shorter periods of time, since there is less downtime/vacancies. Which in turn, less availability = more likely to get fully booked, and the cycle starts all over again.
Just my thoughts, but I find it interesting.