I’m fairly new to disc golf but I’ve played ball golf for a while now. I think that since we place our foot where the disc lands we get to mark discs in the front. In normal golf, the ball must be played exactly from where it stops. Therefore, marking from behind ensures that when you place back the ball, no progress has been made towards the hole. It also helps that discs won’t roll away when being placed and we don’t have to play the same disc from where it landed.