GANs train by fooling AIs, not humans. Fooling humans is a side effect, not the primary thing trained for (mostly because that's cheaper of course). It's just that humans are in some ways different from AIs in terms of fooling.

Looking at the papers I must say I think the ability to fool humans is a scale problem, not a fundamental limitation. Already GAN produced images and sounds survive "normal" human scrutiny: if you have no reason to suspect foul play you won't see it. If you really go looking, you'll see it.