dealer service

How come boat dealers and boat service facilities can't let you bring your boat in and service it while you wait. I don't mean repairs where you do a diagnostic and have to order parts, just regular service. Why is it so hard to have a schedule where they set a time for you to come in with your boat and service (oil changes, etc) while you wait. Also with repairs- they tell you to bring the boat in on this day but they don't even look at until days later. Why not let people have use of their boat as much as possible and schedule to bring the boat in the same day they can start on it?