Shuttle Buses

Hey everyone quick question. I’m new to the city and use the bus service here in town to get around..I noticed that the buses tend to stop running around 8-9pm ish but have seen these shuttle busses running much later was curious as to what they are for. Originally thought they were privately booked for some events but I see them so often I am curious if that’s the case. Any info on this would be great thanks a lot !