First off, the whole point of airborne troops is surprise: you don't know they're coming until they're there. But because Cain arrived 24 hours after the first wave, the surprise was gone. And to make matters worse, the landing zone was some eight miles from the bridge. So, thanks to some incompetent planning by the top brass in England, the Germans knew that Cain and his men were coming, they knew where he landed, they knew where he was going, and they had the wherewithal to do something about it.