"You undid the Kog rework, but why wont you undo these ones?"

The answer simply is that Kog was single-handedly making it impossible to balance every single on-hit item in the game. etc became absolutely impossible to balance properly because they interacted too well with his W. So Riot had to keep these items weak or Kog would be completely out of control. An entire subset of items had to be balanced around a single champion which made them weak on every other champion but Kog for the most part.

The result of this is that Kog's existence was affecting the ability to balance a shit ton of other champions because their build paths were nerfed. Other reworks are more champion specific. Kog's, however, was affecting more than just himself.

So Riot undid it. It was the only option they had. That's why Kog was a special case.