Because LLMs are not humans, and the code they produce will have a different distribution of failure modes than human written code, so attribution is useful info while reviewing?
As I said, disclosure is polite when contributing code to third party projects which will undergo human review.
No need for such things in one's own projects.
This can be largely assumed to be true for any open source code. It's kinda the point of open source.
If there's one thing I learned not to do in open source, it's to assume nonsense like that.
Even with coding agents gaining popularity, many humans still look at the code at some point.