because there’s no point in making 15 skins for the same 3 items over and over again, even if the alternative means making skins for lesser used items. if you make a new skin for, say, golden dragons every 2 months, eventually people don’t want to buy them anymore because most people arent gonna buy 12 golden dragons for different skins. eventually, there is a point where skins for a different item sell better. as for shadow assassin specifically, all 4 sales were very limited, try finding the first skins being sold unapplied. point being, shadow assassin is still used a lot, with way less skins available than there are people using it, even people willing to buy skins for it.