They explain why in their AI policy. It's an ethical stance. Of course they wouldn't notice if there aren't clear signs of LLM-ness, but that's not the main reason why they forbid it.
https://docs.postmarketos.org/policies-and-processes/develop...
https://docs.postmarketos.org/policies-and-processes/develop...
The pollution caused by said revolution is currently putting humanity at a serious risk of world war and maybe even extinction so... maybe they had a point? I'm not taking a strong stance either way here, but worth thinking about the downsides from the industrial revolution, too.