almost any deck running skeletal scrying wouldnt use it
Psychatog got bigger off the yard, and it played Will simply because of how broken it is. 4CC or Keeper or Clinger or whatever used it because not only does it give you a boost, it can totally end your opponnents presence in the game.
Not to mention the obvious synergy between RFG-ing some amazing instant spell, then using Cunning Wish to fetch it again, then re-play it again via Y. Will. I'll even go farther and say you can Wish for it yet again after using it under Y. Will.
Some decks with black don't run it because the game should be over by the time it would be any help. Put it this way, anything that can make Sui win must be too good to be true, and that's what Yawgmoth's Will does. This makes for a need to at least consider it in EVERY deck that runs black.