Omg you can't pay hundreds of thousand ppl just to guard the wall in a freaking cold permanent winter
Why not? And why so many?
Well if it's 72.000 km's, how would you distribute them? First of all you say noone saw it, or wanna talk about it, then you have to guard it pretty good, like 1 man / 1 km? But do you leave them alone? They live alone there? That would be mad, you need to put at least 2. Ok, so that's way more then 100.000 of people. How can you get that? You just take them away from their families? Or do they have homes there and live with the whole family on the wall?
So even if they guard the wall, which they can't, what if someone goes there? They kill him? Or just brainwash and make him their slave?