When you pull into a parking deck either on your ticket or on a sign nearby is a disclaimer that says "park at your own risk" and "management not responsible for stolen or damaged property". What does it benefit the deck owner to put in thousands of dollars worth of cameras?
Because those statements might not protect against a really good tort lawyer?
Because you want to make your parking garage safe for the little old ladies walking to their cars?
Because most insurance companies give discounts for putting up video surveillance?
etc.