Mostly it's just because Joker took the whole 'I'm going to end the world and you can't stop me' spiel a lot more gracefully, and also isn't a Star Guardian familiar. Anything connected to Creation infuriates Steven at this point - especially knowing who she's connected to.

He allows Joker to come up with less complaining, but he doesn't seem actively interested in communicating with him either. Instead he just frowns at the two of them, stepping partly behind the stem of the flower.

"There's no point now," he shouts, his tone sinking with despair. "It's almost over, anyway..."