Clearly it's not as simple as you imagine.
Of course, people may argue that people are not creative, but considering that for a recent court case, it was decided that AI cannot be an inventor, it does matter to that court at least.
Look into a famous recent copyright case, Cariou v Prince. Cariou is a photographer, who made a series of photographs of people in Jamaica an dpublished them in a book. Prince, an artist, liked them, and then treated them as raw material, basically printing them up large, adjusting them, and slapping some paint on top, and declaring it original art - indeed, he called it 'appropriation art' saying 'this is mine now.'
Cariou was upset (very understandably) and sued. The judge found for Cariou, said that Prince was a bullshit rather than a visual artist, and ordered the infringing work to be collected and set fire. Prince appealed, and his appeal succeeded, with the 2nd circuit saying it was "transformative" from the point of view of a "reasonable observer" and therefore fair use, because Prince had added a different aesthetic by turning the portrait photos into oversize graffiti-collage mashups. Cariou gave up at that point as he didn't have the resources or will to fight the case further, and eventually the two artists settled.
Look up the art and see for yourself. I think Prince does have his own aesthetic, but it's a very shallow one that just surfs on other people's work, not very different from drawing glasses and a mustache on top of an existing portrait and saying you made an original work. In many ways, what he's selling is his taste, and the modifications he makes to the picture are just a sort of signature that's semantically equivalent to saying 'I, Richard Prince, approve of this image' - the artist as curator-critic of others' work, if you like.
Back in the computing context, this decision substantially loosens the boundaries of copyright. Found some code you wish you had written and want to put out your own thing, but feel stymied by the license? Just refactor it, add a bunch of sassy comments, and make the interface (whether, CUI, CLI, or API) aggressively different - not necessarily better, just distinctive. If it's fun and whimsical, make it corporate and bog-like. If it's scientific and functional, make it silly and juvenile. Just futz with it a bit until you can plausibly say you either made it better or easier to read or more accessible/intercompatible in some way. Hell, slow it down a bit and say your code smells better because it cooks the JSON longer, and generates a bunch of 'useful' statistics that might seem superfluous to the original designers but are essentially interesting to you. You'll probably get away with it.
Copilot is pretty commonly just copy/pasting. You can get it to spit out exact copied code, including comments.
p.s. "it's not as simple as you imagine" is pretty dickish. Why include that?
I think this is the crux. It doesn't matter that they used GPL code for training. It only matters if someone uses CoPilot to make a close copy of that code.
Fortunately Copilot is actually not commonly just copy/pasting. They did a study on that if you search for it (admittedly not an independent study but it's the only one we have).
> Why include that?
Because so many people are making the assumption that the law agrees with their overly simple interpretation before it's even been decided. It's a bit tedious.
