The hotels only make money on pre-pay if enough people who pre-pay change their plans and cancel (but since it's prepay they can't get a refund), because then the hotel can collect double for one room (the original guest who pre-paid but coudln't show up, and the new guest who actually used the room). Perhaps therefore pre-pay is only available at those locations where the hotels have made money on it (pre-pay customers cancelling without getitng their money back and thus the hotel being able to get two payments for one room), and not avialable at those hotels where they couldn't (or didn't want to) get that to work?