I'm very late for this..

This isn't the complete reason but a certain person was going to do full AD illaoi. Can you imagine the carnage of Sword of the occult fully stacked on her?

Go look up UberDanger on youtube and imagine you were on the receiving end of that in a ranked game. Plus Riot is making a lot of AD reliant/dependent champs recently so I guess they did it to stop people crying about every single AD champ is broken. Example + + +