The GPL relies on copyright ownership for its effectiveness, and copyright ownership of LLM output is a legal gray area right now.

"...prompts alone do not provide sufficient human control to make users of an AI system the authors of the output." [https://www.congress.gov/crs_external_products/LSB/PDF/LSB10...]

If code generated by LLMs turns out to be effectively public domain, that could seriously water down the legal standing of copyleft licenses. Fortunately there is still enough human-authored code that long-standing projects as a whole are not at risk of losing all copyright control, but as more LLM-generated code is incorporated, and human authored code is deleted, the copyright slowly gets washed away.

Having said that, I suspect the big AI companies have enough lobbying power to influence the legal system and lawmaking in the future.