You step in between two panels of the door and push on the panel in front of you. The revolving door begins to rotate and once you reach the inside of the building. You step out into the lobby. Therefore, the closer you are to the pivot, the more force you must exert to result in a certain amount of torque. The door tends to keep on turning after you stop pushing, and it can bump you if you re not careful.
Angular momentum keeps it moving.
The people who built the revolving door wanted it to be easy to start and stop. Remove the mass from the outside edge. This causes the greatest decrease in the moment of inertia of the door, so it requires less torque to set it in motion and to stop it.