[ahtihn]

Code is purely functional and is copyrightable so why would a prompt not be?

A prompt has essentially the same purpose as code, especially when it's long and precise.

[kopecs]

Code is not purely functional. If it is, it is not copyrightable (at least in the US; probably true elsewhere but I am less sure) [0]. I would not expect most prompts to be purely functional.

[0]: https://www.copyright.gov/circs/circ61.pdf