Hello, Because if the lower anchor fails there is an important friction point on the rope that could damage it. So the belay must be also bombproof. In many case, on routes the top rope belay is usually placed in a high point on the cliff, this is a belay station with always two anchors, but to safely reach it from the top you would have to use natural belays (on trees) to reach the belay station and install your ropes. Thank you for your participation Sincerely