Why is there no interior door to close the cabin?
The cab is equipped with protection photoelectric cells protection on the side of the moving wall. Any movement that breaks this cell field (for example, when a person or object passes nearby and is detected by the cells) blocks the movement of the cabin. As soon as the cell field is restored, the private elevator can restart.
Clearly, this presence detection system prevents the cabin to move if the door is not properly closed, and all passengers inside!