Everything in art is made with a specific design in mind.
An artist doesn't just pick random collors of clothes and acessories for their character, they choose, either conciously by trying to evoke particular feelings, or not, in which case their work might be derivative, but still original and intentional.
In writing, the words used to describe a place or person, or the feelings trying to be transmited through a bit of poetry are all things you choose, and again, you do so intentionaly trying to evoke a particular feeling, or unintentionaly, letting your influences control you.
The heartfelt song the dwarfs created to stave off the dread of living in a hole with no light or warmth is lost if those words were not handpicked for that feeling in particular, but instead are just randomized words that sound hot and longing.
The beauty of the dress worn by the princess and nuanced details that tie into the setting and the care of the artisan are lost if you just say, its 'sexy and red and she had a flower on a hairpin'... It loses that provocative red tone the princess choose to spite her mother, and the large cleaveage she choose to defy the customs, or the narcissus on her hair that is a statement of a mockery of those who would challenge her.
AI destroys that process
It removes the choice for choice and replaces with objective and repetive things other people used before in more sucessful media.
If you use AI to make a calculation you lack the proper knowledge, sure its ok, math is hard.
but anything creative is meaningless if not made by an individual who chooses their purpose.
Might be good enough for a souless corporation who only cares for deadlines and delivering a 'just barely passable' product, but not for a human being with a soul who wants more out of life than just laying down and waiting for inevitable doom.