Because driving a bus takes so much skill and expertise. Especially when your getting paid 6 figures to do it.
That's $41,400 for about two hours work a day - ten hours a week - 34 weeks a year ( school years are short) and that works out to $121.76 an hour for the limo company... or 'mother' needing a part time job... Not bad wages for anyone other than a union goon.