Many on-site guests choose to drive to the parks, so Disney provides service back to the parking lot until well after the park closes. Guest can be in line for a ride minutes before closing time and may not get out of the park until an hour later.
That being said, allow me to offer my advice. When we have a car, we might drive to Epcot, DHS, and DAK. But driving to and from MK is a pain because the lot is huge and distant. The requires driving to the MK AND waiting for a parking lot tram AND time on the tram AND waiting for a ferry or Monorail AND time on that transportation. In comparison, MK typically has the most frequent bus service from resorts, and the buses go to a bus station relatively close to the MK entrance.