When the seat belt light goes off, some people get into the aisle. They must take their bags down. (If they put their bags someplace they can't reach them, they have to leave the aisle.)

When the door opens, everybody in the aisle just walks off the plane. Do not stop to let someone go in front of you.

Look at it from the viewpoint of the doorway: at any given time, either there is a person going through or a gap. When enough people have gone through, the plane is empty. The total time taken is the time for all the people plus all the gaps, therefore we want to minimize gaps.

Gaps are created when the person at the front of the line stops moving. Whether that's to take down the bags he put 15 rows ahead of him, or to let someone slowly climb into the aisle and then get down their bags, doesn't matter. Creating gaps slows the plane emptying.