Reverting champion nerfs after item changes

When champions synergize extremely well with an item, especially in an overly oppressive way, the champions often see changes to the way their abilities and base stats scale. After a few patches or even a season, the items will see nerfs after supposedly a large enough sample of data has been analyzed. The items are still a good purchase after this, but they aren't in their old "must rush first" state. I know I see sarcastic posts referring to this as champs being "Sejuani'd", and I've never seen a rebuttal from Meddler or any other Red. Once and for all, why don't champ nerfs get reverted once an item receives nerfs/changes?