So, as it stands, sleeveless armor cost a lot less resources to make than they return. Sleeveless Trenchcoat takes 9, and gives 13.
Also the skill levels for making the the sleeveless items from scratch should be on the same level as the the base item for balance reasons. Also by the time you get to such a high level of sewing for survivor gear, it makes little sense that the sleeves would provide so much of an issue that you need a whole level to be able to make it.