Although the question suggests that it is a fact that the Great Wall of China is visible from space, it actually is not visible to the naked eye from space.
According to NASA themselves, the Great Wall of China is not even visible to the naked eye when in low-earth orbit. Yes, the Great Wall of China is a gigantic and long piece of ancient human architecture that stretches 13,170 miles, but this does not mean that it must be visible from space.
In fact, the Great Wall of China is actually very thin, although tall and long, so it is quite difficult to see from space. This is why it cannot be seen by the naked eye, since it is narrower than a lot of rivers that also cannot be seen from space.
This is all according to astronauts who have actually been into space and looked down on the earth. So, their testimony is obviously trusted, since they have the means of zooming into the earth to see what is visible from space.
If you were to use a zoom lens on a camera when you were up in a space ship in space, you would be a lot more like to be able to see the Great Wall of China.
But the reality is that it would still be difficult to spot, even with a zoom lens, because it is an extremely thin piece of man-made architecture in comparison to the size of the earth.
This means that things like the Houston airport are more likely to be see if you zoom into the earth with a camera, since it is a larger building and area overall.
You are also more likely to be able to see roads and larger highways that lead into big cities before you see the Great Wall of China as you zoom into the earth using a space camera.
This is because some roads are built into hillsides and even carved into them, so the alteration of the natural landscape is a larger blot on earth that is visible from space with a zoom lens.
But since the Great Wall of China hugs the land, even though it is man-made, it is less visible from space using a space camera with a gradually zooming lens, let alone using the naked eye.