Because AI-assisted code is most probably already present in devices they use.
And I dare say that even for PostmarktOS:
1) There's no way they can prevent AI-assisted code to reach their codebase.
2) They will most probably change this policy in the future lest other forks/projects outpace them in terms of utility and they get reduced to a carriage in a car world.
The stance is to deter random vibe-coders trying to resume-max by submitting PRs to known open source projects. There are so many of them rn. Hopefully by making it clear (some of) them will realize doing that is just wasting their tokens.
But to be clear their AI instance is as clear-cut as can be. Their instance IS INDEED to "prevent AI-assisted code to reach their codebase".
> The following is not allowed in postmarketOS:
> Submitting contributions fully or in part created by generative AI tools to postmarketOS.
source: https://docs.postmarketos.org/policies-and-processes/develop...