[{quoted}](name=Katrina Steiner,realm=NA,application-id=3ErqAdtq,discussion-id=rUi5EjTP,comment-id=0001,timestamp=2015-11-06T05:04:30.436+0000)
They aren't needed is a silly argument, A better question is why does riot spend time developing a mini mejai's item and also changes mejai's, but does not make the same changes for the AD version of the item.......
Mejai's is used by champions who have much greater safety (Janna, Lux, etc), so it can be balanced around them keeping the stacks. It's a reasonable pickup on such champions if they want a cheap item that grows to give respectable AP.
SotO, on the other hand, who is this item ACTUALLY good on? AD assassins or ADCs who are both liable to get blown up at a moment's notice with more frequency than the likes of the Mejai's users. Plus, there's the fact that AD champions generally need more than just AD to function well. They want penetration, life steal, a bit of CDR, the AoE of Tiamat and/or critical chance, plenty of AS for ADCs... And SotO only provides AD and a paltry AS buff if you max it.
There's no real way to make SotO a choice to consider outside the realm of someone snowballing into insanity. At which point they could build any other AD items and get more benefits.