Question, why doesn't Illaoi E apply DFT but her W does?

She applies DFT to the spirit of the champion she landed her E on but not the actual champion, isn't she technically dealing spell damage to the enemy champion?

Also why does her W apply DFT but Garen Q, Darius W, and Nasus Q don't? It is still an auto attack with bonus damage like them.

And before you downvote or say Illaoi doesn't deserve buffs or "good, fuck that champ" just know that I'm asking a question, not making a buff Illaoi post.