Because AI Art is outsourcing the creativity part to a machine. You're not creative if you use AI image generators. They CAN be used creatively but their use in and of itself isn't creative because nothing is being created, only imitated, only aproximated, no real human input except text.

So, no real human input apart from the human input? Out of curiosity, have you ever tried using an AI generator yourself? There are several available to use for free online.