I don't think anyone seriously thinks that is required. The real issue is that these models can reproduce code they've been trained with and then you do need to be aware of the license. That would be fine except as far as I know none of the existing solutions warn you that the code they've produced is the same or very similar to copyrighted code they learnt it from.

That's the main difference from a human learning from copyrighted code (which is totally legal). If they have a good memory they might be able to reproduce copyrighted snippets, but they would usually (probably not always!) know they are doing that.