At the perfume bottle, the neck and the cork are carefully polished at the point of contact. Why?

Carefully grind the neck and plug at the point of contact in order to make the minimum possible gap between them. With a minimal gap, it is more difficult for perfume molecules to penetrate between the neck and cap and leave the bottle. So that the molecules of the substance from which the perfume is made, as a result of the chaotic thermal movement, do not fly away from the bottle. So that the perfume does not evaporate from the bottle closed with a cap.