The problem is that it's not the user of the LLM doing the reproduction, the LLM provider is. The tokens the LLM is spitting out are coming from the LLM provider. It is the provider that is reproducing the code.
If someone hires me to write some code, and I give them GPLed code (without telling them it is GPLed), I'm the one who broke the license, not them.
If someone hires me to write some code, and I give them GPLed code (without telling them it is GPLed), I'm the one who broke the license, not them.