Yes, that is a good question and one that could and maybe should be asked of Roberts bus company on Maui.  My guess would be that many, who are not currently driving school buses are "on call." What does not make sense is that Ground Transport is willing "to fly in" bus drivers from O'ahu for the work; not to mention the facts that GT should have known ahead of time, whether or not they would have had enough drivers for the new school year, before hand.