I think it's similar thing with hands, we immediately see the problem with the hands because we know how they work and recognise when the generated hands wouldn't work.

This expands to all kind of machinery actually. The moment you start reasoning about the output it falls apart. I only assume at some point there would be another AI model which is trained on how things work and will guide the current AI stuff.

Like the way ControlNet guides StableDiffusion to produce output the way the user desires.