Why do players not build Iceborn Gauntlet on Illaoi?

So I was wondering about this, because it seems like an absolutely perfect item for her. the vast majority of Illaoi's damage comes from passive tentacles which swing at enemies who are hit by her W auto attack modifier. The tentacles are slow and easily avoided by most players with a competent reaction time, and because the tentacles aim based on auto attack'd enemies rather than them being skill shots you can't lead them or anything of the sort. Illaoi has the second highest base attack damage in the game and her W auto attack modifier is on an extremely low cooldown. Iceborn gauntlet gives her 100% base AD and a 30% slow on every W, which causes tentacles to slam on slowed targets unable to simply walk out of them.

I don't know, it seems like the item is literally tailor made for every aspect of her kit, but nobody buys it on her. Is it solely because both it and cleaver have 20% CDR, so if she buys IBG she ends up radically overcapping CDR because she also wants spirit visage or Death's Dance?

Will wee see IBG on Illaoi suddenly spring up when transcendence comes out during the rune rework?