Because the carbon of the wick comes into immediate contact with the oxygen of the air.
257. Why does holding a candle "upside down" put it out?
Because the melted grease runs down too rapidly, and at too low a temperature to undergo combustion. It therefore reduces the heat, and extinguishes the flame.
"Lord, what is man that thou takest knowledge of him! or the son of man, that thou makest account of him."—Psalms cxliv.
258. Why is it more difficult to blow out the flame of a candle with a cotton wick than one with a rush wick?
Because the cotton wick imbibes more of the combustible materials, and holds in its loose texture the inflammable gases in a state ready for combustion.