Deadman's Plate Crushing Blow Used Up On Illaoi Tentacles

Had the awkward experience of the slow and damage proc. on DMP being wasted on Illaoi's tentacles. It isn't wasted on plants or fruits so this makes no sense to me.

I think the item could use a tiny bit of help anyway but that's a bit off -topic: https://boards.na.leagueoflegends.com/en/c/gameplay-balance/0x5h63dx-deadmans-plate-is-still-weak-a-suggestion-more-defined-identity?show=new