I do not know why but some 3d printer do not come with a layer fan. In my opinion, layer fans are must haves in every printer. The reason is it once the molten/melted pla is deposited on a layer it will tend to ooze if it Is still warm. Oozing plastic will result in bad layer construction in 3d prints.
in the video you can see the drastic difference in print quality with and without a fan.