Ai dialogue sucks

Why does the conversation sucks on ai written fanfiction. I just read a conversation about Harry talk to Mrs figg and it went like this

Mrs Figg stood upon the pavement in a faded purple dress, two shopping bags hanging from one arm. Her grey hair had been pulled into a loose knot which listed towards her left ear. A net bag of oranges pressed against one hip. The top of a cat's head protruded from the other bag.

Harry blinked.

"Is that a cat?"

Mr Tibbles lifted his face between a packet of tea and a tin of sardines. He regarded Harry with yellow-eyed disapproval.

"He didn't want to remain at home," Mrs Figg said.

"So you took him shopping?"

"He took himself. I found him in the greengrocer's."

Mr Tibbles sneezed.

Harry set the shears down. "Did he buy anything?"

"He disapproves of their fish."

"That isn't a no."

Mrs Figg shifted the bags. "You look dreadful."

"Good morning to you too."

"Have you been sleeping?"

"Yes."

It came automatically. Mrs Figg looked at him.

Harry had known her for most of his life. The Dursleys sent him to her house whenever they wanted an outing which would be improved by his absence. His childhood memories of those visits contained stale cake, photographs of cats and cabbage boiled beyond recognition.

She had always seemed harmlessly peculiar.

During the past year, Harry had begun to suspect the peculiarity required more effort than he had realised.

"You have shadows under your eyes," she said.

"I have eyes under my shadows."

"That is not reassuring."

"It wasn't meant to be alarming either."